THE ESSAY BUNNIES, THEY ARE EVERYWHERE D: Also I am trying to figure out why a normally "RAR HUMANS KILL THEM ALL >D" character is chatting with children orz.
SO. In the TV special made for the alternate future timeline 17 comes from, 18 explicitly states "Whenever we see humans, it angers us. We hate humans." However, the way she says it makes it sound a lot less like "hate" as in RAGE AND ANGER AND I WILL TAKE STUPID CHANCES IF IT MEANS DESTROYING YOU IN THE MOST MESSY WAY POSSIBLE and more like... "ewww, I hate spiders. :/" In addition, the whole killing humans thing didn't start until after they killed Dr. Gero. In the future timeline, they spent a good deal of time with him before the breaking point came; enough for him to start actively working on Cell (which started several weeks before their first attack). Headcanon says that during that time they got rather prejudiced about humans via psychological conditioning from Dr. Gero ("Humans are weak and worthless! You two are the world's most powerful creation, worth far more than the lives of any mere human!" etc.), as that's one of the main places the two timelines split off with regards to what happened to 17 and 18 specifically.
17's take on humans is somewhat similar to an average human's view on cockroaches: they're messy, annoying, suprisingly hard to kill, and it's very satisfying when you squish them. Of course, humans are sentient, but that just adds to the fun. After all, human behavior is much more complex than cockroach behavior (and to him, just as incomprehensible). Not to mention they make cool things (see: cars, motorbikes, videogames, amusement parks, etc.) Compare this to 18, who views "the fun part" as killing them. After they're dead, there's no point in sticking around any longer (whereas 17 will happily spend his time blowing stuff up and roaming around in the ruins).
Powerful humans (or saiyans. Saiyans are really just humans with bad hair |D) get somewhat more special consideration. As toys, they last longer; if he's careful about not breaking them too badly, then they even come back to play more :D!
EFFECTS OF CAMP ON THIS: 17's first reaction to camp was something along the lines of "Oh sweet! New toys... and these ones aren't afraid of me! I WILL TAKE GREAT PLEASURE IN MAKING THEM FEAR ME huhuhuhu-- o crap. 18 will kill me if I start without her :(" However, the lack of screaming and running when he started ~watching people~ intrigued him, so he decided to stick around and see what was up.
Pre-getting his butt handed to him by Vegeta, 17 decided he had no desire to tell 18 about this place-- or blow it up, for that matter. THERE ARE COOL PEOPLE AND THINGS HERE and she'd just mess it all up. Probably for revenge for all of the times 17's done the same to her, which just makes it worse :< Post-getting himself owned? Oh HECK no. Cool place or not, he needs to warn his sister that SIS THERE IS A SCARY MAN WHO IS GOING TO KILL US. Once he's past his BAWWW THIS ISN'T POSSIBLEEEEEEE/my life is pain , he's going to try to get out of there to go grab 18 and go into hiding. cue attacking the barrier with accompanying WHY ISN'T IT WORKING D:
TL;DR I ENJOY PLAYING 17 AND WANT TO BABBLE OUT EVERY LITTLE THOUGH ABOUT HOW I'M PLAYING HIM god I love this boy's headspace. IT'S FILLED WITH MURDER AND HYPERNESS