I was reading something on a list today about Slytherins being evil, perhaps specifically due to the fact that their house was based on Pure bloodlines (something that's changed to "ambition and cunning" by Harry's first year, though was possibly pretty unremarkable an idea thousands of years ago-Durmstrang doesn't even accept Muggleborns iirc). Anyway, there was the comment, "Unless of course one considers Draco to be a good Slytherin, which I most definitely don't." Somewhere else there was another essay on Slughorn being the "true" Slytherin--what they were before Voldemort, and so what they should be. I've written about the idea of Slughorn as "The Good Slytherin"
before, and this is sort of the next step from that. Because I was thinking that while at this point I wouldn't say Draco was a Good Slytherin (meaning the Slytherin who is a good person), I did think he had potential in ways that Slughorn really did not.
If the sickness in Slytherin stems from the blood purity issue, it seems that the way to show it would be to show its destructiveness (which I think JKR tries to do with the Blacks, for instance). And in order to show a Slytherin without this idea...well, you could do the fanfic thing of just creating a Slytherin who doesn't have it but is still tight with the Slytherins, but as I've said in the past that seems like a cheat to me after the way it's been set up, because it sticks a non-Slyth decoy into the house so that Harry can collect a green and silver tie for his army without having to deal with the house as its been defined. There's nothing to stop the author from doing it that way, but it doesn't really show how Slytherin can change. It's more hoping for a purge of Slytherin rather than a new Slytherin--and that's uncomfortably close to, well, some ideas on the other side. It's also what Harry would want, so it's too easy.
So here's why I think Draco has more potential than even a better person like Slughorn. (And remember I said potential, so this isn't an argument that Draco's already redeemed in the fandom sense, nor a love letter to Tom Felton) I take Harry's note that Slughorn seemed "a little too surprised" about Lily's blood given her talent very seriously. I think Slughorn buys into the Pureblood ideals he was probably raised with. JKR doesn't really go into the history of this sort of thing, but she often, imo, falls back on hints that the WW's history mirrors our own. So its society in the 1950s possibly had more obvious distinctions based on blood. It was simply more acceptable to be openly discriminatory in conversation etc. I seem to recall that Slughorn's club in Tom Riddle's years were mostly boys, reflecting the same shift towards co-ed things that I think of in our world. It was just part of that whole stereotype for there to be boys there. I wouldn't be surprised if they were all from old Pureblood families as well.
Someone described Slughorn as trying to get away from that mindset, but I don't he's trying all that hard. It's more like he's just going with the flow, imo, softening and stretching his ideas over the years. Yes, he has non Purebloods in his group, but that doesn't mean he doesn't see a difference between them and the Purebloods. One can, for instance, be a completely racist owner of a team and still pay top dollar for non-white athletes. That's what keeps Slughorn from being that hopeful, to me. He's older and he's made his way. He fawns over Lily and seeks out Harry's Muggleborn friend Hermione, but I think that's more his changing with the times than any inner drive to be fair. He's made allowances and rationalizations. He's polite and welcoming, with these uglier possibilities just peeking out at odd moments. I think he'd be just as happy with all Purebloods. It's certainly better than nothing, but it suggests, to me at least, someone who clung to those beliefs enough to stretch them with the times rather than abandon them.
Obviously Draco hasn't abandoned these same ideas at all--far from it. Perhaps he never will and the idea that he would even consider it has never entered JKR's mind. But based on what's in canon now, she's laid the groundwork for a change here. I don't mean that he's been changing already or anything like that. What I mean is, look at his character, especially in contrast to some of the older people. Draco is not the polite bigot. By being more open and simple, Draco's bigotry is easier to see and address. He's not Lucius who uses the term "Muggleborn" to describe the person Draco should be ashamed of being bested by in an exam and speaks wistfully of changing times and laws while being a DE. Nor is he Slughorn trying to sound forward-thinking to Harry because his mother and best friend are Muggleborns while surely also smiling benignly at any Mudblood jokes Blaise Zabini might tell.
No, Draco's pretty black and white about this: filthy Mudbloods, purge the world of them, mind the smell, don't slime up my hand. It's a lot uglier, but it's also kind of betting it all there, like there's a lot riding on this. And while Draco has certainly never shown any sign of doubting or letting up, I have really started to see more of an arc between him and Hermione than I did before. It used to be everyone always just concentrated on his "warning" Hermione at the QWC, which I didn't think he was doing--and still don't. But I am beginning to see something potentially set up in his dealings with Hermione, and it's pretty simple. He wants to hate her, but he keeps having to face this disconnect between what she's supposed to be and what she is.
CoS is the first book where they have something to do with each other personally, starting before school. Lucius makes a crack about Draco's grades being at the "thief and plunderer" level. (I'm confident after HBP that we are meant to see Draco as basically a good student--not a genius, but up there in the class.) Draco brings up "that Hermione Granger" as a teacher's favorite, using her as a defense for himself. Lucius coolly says he'd have thought Draco would be "ashamed" that a "Muggleborn girl beat him in every exam." This makes Draco abashed and angry. So there's the gauntlet laid down, ironically by Lucius himself. In trying to shame Draco into living up to his blood, he's laid out the basic fallacy of his belief system. If Purebloods are so much better at Magic and superior, why is Hermione top of the class? Will Draco see that the Pureblood Supremacy idea has been falsified and reject it? Or will he try to force the world to conform to those ideas?
He'll try to force the world to conform. When Hermione humiliates him in front of the team, he calls her a Mudblood, trying to insist she is nothing and can never be, no matter how she does in school, because of her blood. This, unsurprisingly, is the book that introduces the whole "cleansing of the race" idea, and Draco wants Hermione to be the first to go. That would certainly show who was superior. If he can't beat her on exams, this shows that it doesn't matter. Draco's totally on board with the program, wishing he could help the heir--be Robin to Voldemort's Batman. Hermione, meanwhile, is cooking Polyjuice to get into the Slytherin Common Room, having also identified Draco as the face of Voldemort's beliefs at her school (though she, the Muggleborn, doesn't gain access to Slytherin herself, interestingly). Draco also brings up Myrtle, though at that point no one knows that's who he's talking about, when he says the last time the Chamber was opened, a Mudblood died.
For the next few books Draco is still supporting Voldemort, though we don't get too many scenes of Draco specifically angry at Hermione. (There is the slap, which never gets connected to blood issues.) We do get the Death Eater scene at the QWC where he draws the connection between Hermione and the Muggles--he sees her connected to them in ways Harry and Ron don't. GoF also has my favorite new wrinkle to their relationship. On re-reading I have become rather convinced that the Potter Stinks badges, which flash "Potter Really Stinks" when they're tampered with, were made by Draco with the assumption that Hermione would try to turn them against him, and booby-trapped with that in mind. It's not something I can prove in canon at all-Draco doesn't say he made them or had them made--I don't think it's a big stretch either. What I like about it is that it does suggest that same competitiveness on Draco's part. Like he'll say he's better than Hermione loud and clear, but he would like to actually prove it, perhaps to himself more than anyone else.
Draco's mostly waiting in the wings in OotP, being set up for his own number in HBP. In that book Hermione makes it into the Slug Club--but Draco seems to have been inducted into his own Inner Circle as well. Obviously there you've got Draco actually doing what he wanted to in CoS, helping the Heir kill someone, and there he is linked with Myrtle, another Muggleborn. Draco may not know about her bloodline, but he probably didn't ask either. The main thing in HBP is that in Draco's final dialogue with Dumbledore, a scene I assume should be important given that it's the thing JKR wastes much of Dumbledore's last breath on, Draco reveals he's been getting ideas from Hermione --the coins and the Potions both. He refers to her as "that Mudblood Granger" and Dumbledore tells him not to use that word. Draco chides him for caring about language when he's about to die and Dumbledore (who is about to die, but knows it won't be by Draco's hand) says that yes, that still matters.
Now, do I see this as some big turnaround for Draco? No, HBP just gets Draco to the moment where he's potentially going to make some choices, stop following a script. But there is enough of a foundation laid (not much needed, really) for him to have to choose one way or the other--Pureblood ideology or not--in a way that slippery Slughorn or even Lucius maybe never had to choose. At this point that kind of choice seems like what Slytherin as a house would have to symbolically go through. It's not just somebody showing up without those bad qualities to be a Harry supporter, and it's not getting rid of it only through death, jail or exile (the last two suggesting they will return ASAP).
This would possibly finally ask the unasked question of the whole thing: how does one come to see this line of thinking is wrong? Did Snape go through the same thing? Maybe, maybe not. Maybe Regulus didn't either. It could sort of be the thing that's failed in the past, that side-switching concentrated on the symptom instead of the problem. Sirius says lots of people agreed with Voldemort's ideas but changed their mind when they saw what he was willing to do to achieve power--iow, they liked the Pureblood superiority idea, but didn't like Voldemort. Turning from Voldemort is the temporary, superficial solution. A far more hopeful future would depend, imo, on the idea that someone who actually believed in these ideals could come to no longer believe in them.
This isn't a prediction for anything in canon--no idea which way it will go. But whether or not JKR chooses to use it, I think she has created one character to play this out on. It would be a good reason for creating Draco the way he is, as opposed to making him a slicker, cooler Slytherin villain. That Draco could put on a face of thinking Muggleborns were equal while still believing them inferior underneath the surface and so keeping a little bit of Voldemort alive.