Thoughts
I had some thoughts while rereading Sorcerer's Stone, specifically on houses--specifically Slytherin and Gryffindor.
I think Gryffindors can be selfish and even cruel without much difficulty. Harry and Ron--Ron, especially--are seen as being rather undeservedly cruel to Hermione before the troll incident. Gryffindors also don't care much about rules so long as they don't get caught.
Slytherins, on the other hand--well, let me explain something about myself first. I don't like to lie if I can help it. If I at all can, I will lead someone to believe something that is false by only stating the truth. Like in this situation (which is, btw, false):
Person 1: Didn't you say you had a boyfriend?
Person 2: Yeah, I did.
Now, what Person 2 isn't saying is that perhaps they said that two years ago, or that perhaps they were outright lying when they said it. They didn't actually say they have a boyfriend now.
And that's how I imagine Slytherins to be. They operate within the rules if at all possible, and only venture to break or bend them when there is no other possible choice.
And perhaps that is why Slytherins see the slight favor McGonagall gives the Gryffindors as unfair, while the significant favor Snape heaps on them is not unfair: Harry isn't in trouble for having a broom when it's quite distinctly against the rules, and in fact it was a teacher's idea! Gryffindor could have waited another year for Harry, but they didn't. On the other hand, Snape's favor manifests as more House points and better grades. And of course the Slytherins feel they deserve these. Slytherin fairness isn't "equal shares for everybody," it's "allotment based on how deserving one is." There was no reason Harry 'deserved' to be on the House team besides talent and a misbehavior (which really ought to count against him); whereas the Slytherins deserve House points and better grades for operating within the rules and for simply being smarter.
I guess there didn't end up being much point to this. I was just kind of typing, didn't have any organization. tl;dr: Slytherins operate within the rules whenever possible, exploiting loopholes; Gryffindors are too blunt-minded to look for loopholes and instead just break rules.
Added: Thoughts on Ravenclaws!
In The Shadow of His Wings by Mirabella (WIP), Harry as co-DADA teacher with Draco reflects that he now understands, miserable as it was, why Gryffindors took their double classes with the Slytherins: The idea of pairing Slytherins with the cold brilliance of Ravenclaw is terrifying, and the Slytherins would absolutely destroy the Hufflepuffs.
Even before tSoHW, I saw Ravenclaws as people who valued intelligence and knowledge above all else. They are not counted among the ambitious because their ambitions involve knowing as much as possible; they are not counted as brave because they would rather research and analyze a problem rather than rush in where angels may or may not fear to tread; they are loyal, but their loyalty extends more to their own intellectual interests than to the people around them. Their morals involve only those they create for themselves, whereas Gryffindors and Hufflepuffs are expected to have society's "good" morals. I am reminded of a quote from If You've a Ready Mind by Maya (sadly, no longer online due to the author's transition into the published world--go here and learn about her book coming out next June!), repeated over and over by a Draco who was sorted into Ravenclaw and hoped for his father's approval anyway: "Knowledge is power." Ravenclaw as a house (not necessarily as individuals) is coldly brilliant. I believe I would be a good Ravenclaw because, while I have many Slytherin traits, my favorite thing about myself is that I am brilliant. Ravenclaws, in my opinion, are Ravenclaws not necessarily because they are intelligent, but because they value knowledge and intelligence highly and, if not naturally gifted, are willing to work hard for it. Ravenclaws are bound only by their intelligence and creativity--or rather, everyone is bound only by their intelligence and creativity, and Ravenclaws seek always to expand those borders in their own minds.
I read a fic somewhere, I can't remember where or when, but it involved Draco as an assassin for the Ministry. He has no qualms with killing those he is instructed to kill, but if he can help it he won't kill pets, spouses, children, et cetera. When Harry is told of these morals, Draco says "At least I stick to mine," continuing with something that shares its essence with "You may have 'better' morals than I do, but you can't stick to them." This is how I believe Ravenclaws approach their morals.
tl;dr: Ravenclaws are not, like Gryffindors and Hufflepuffs, bound by society's morals, but the morals they mke for themselves.
I think Gryffindors can be selfish and even cruel without much difficulty. Harry and Ron--Ron, especially--are seen as being rather undeservedly cruel to Hermione before the troll incident. Gryffindors also don't care much about rules so long as they don't get caught.
Slytherins, on the other hand--well, let me explain something about myself first. I don't like to lie if I can help it. If I at all can, I will lead someone to believe something that is false by only stating the truth. Like in this situation (which is, btw, false):
Person 1: Didn't you say you had a boyfriend?
Person 2: Yeah, I did.
Now, what Person 2 isn't saying is that perhaps they said that two years ago, or that perhaps they were outright lying when they said it. They didn't actually say they have a boyfriend now.
And that's how I imagine Slytherins to be. They operate within the rules if at all possible, and only venture to break or bend them when there is no other possible choice.
And perhaps that is why Slytherins see the slight favor McGonagall gives the Gryffindors as unfair, while the significant favor Snape heaps on them is not unfair: Harry isn't in trouble for having a broom when it's quite distinctly against the rules, and in fact it was a teacher's idea! Gryffindor could have waited another year for Harry, but they didn't. On the other hand, Snape's favor manifests as more House points and better grades. And of course the Slytherins feel they deserve these. Slytherin fairness isn't "equal shares for everybody," it's "allotment based on how deserving one is." There was no reason Harry 'deserved' to be on the House team besides talent and a misbehavior (which really ought to count against him); whereas the Slytherins deserve House points and better grades for operating within the rules and for simply being smarter.
I guess there didn't end up being much point to this. I was just kind of typing, didn't have any organization. tl;dr: Slytherins operate within the rules whenever possible, exploiting loopholes; Gryffindors are too blunt-minded to look for loopholes and instead just break rules.
Added: Thoughts on Ravenclaws!
In The Shadow of His Wings by Mirabella (WIP), Harry as co-DADA teacher with Draco reflects that he now understands, miserable as it was, why Gryffindors took their double classes with the Slytherins: The idea of pairing Slytherins with the cold brilliance of Ravenclaw is terrifying, and the Slytherins would absolutely destroy the Hufflepuffs.
Even before tSoHW, I saw Ravenclaws as people who valued intelligence and knowledge above all else. They are not counted among the ambitious because their ambitions involve knowing as much as possible; they are not counted as brave because they would rather research and analyze a problem rather than rush in where angels may or may not fear to tread; they are loyal, but their loyalty extends more to their own intellectual interests than to the people around them. Their morals involve only those they create for themselves, whereas Gryffindors and Hufflepuffs are expected to have society's "good" morals. I am reminded of a quote from If You've a Ready Mind by Maya (sadly, no longer online due to the author's transition into the published world--go here and learn about her book coming out next June!), repeated over and over by a Draco who was sorted into Ravenclaw and hoped for his father's approval anyway: "Knowledge is power." Ravenclaw as a house (not necessarily as individuals) is coldly brilliant. I believe I would be a good Ravenclaw because, while I have many Slytherin traits, my favorite thing about myself is that I am brilliant. Ravenclaws, in my opinion, are Ravenclaws not necessarily because they are intelligent, but because they value knowledge and intelligence highly and, if not naturally gifted, are willing to work hard for it. Ravenclaws are bound only by their intelligence and creativity--or rather, everyone is bound only by their intelligence and creativity, and Ravenclaws seek always to expand those borders in their own minds.
I read a fic somewhere, I can't remember where or when, but it involved Draco as an assassin for the Ministry. He has no qualms with killing those he is instructed to kill, but if he can help it he won't kill pets, spouses, children, et cetera. When Harry is told of these morals, Draco says "At least I stick to mine," continuing with something that shares its essence with "You may have 'better' morals than I do, but you can't stick to them." This is how I believe Ravenclaws approach their morals.
tl;dr: Ravenclaws are not, like Gryffindors and Hufflepuffs, bound by society's morals, but the morals they mke for themselves.