I don't think she'd go on a mass murdering spree. You'd have a lot of difficulty making that IC. She is still a compassionate person and she's good friends with Hermione, who's Muggle-born, so she probably knows a bit about Muggles. Her father is fascinated with them, so I doubt Harry being killed by one would make her hate them all. I'm not even sure she'd kill the Muggle who did it, although she'd definitely would try to hurt him. She probably wouldn't use Avada Kedavra, but if she used another spell and in her anger made it too strong she could end up killing him all the same. I doubt she would feel good about it later though. She would, in my opinion, deal with his death in another way, but I can see her resenting Muggles for a long while, maybe falling out with Hermione over it, and that would make her coping with the situation even harder.
As for the wizarding world taking sides; surely there are still Pureblood maniacs left over so they might try to exploit the situation, using it as an excuse. Muggle-borns and Half-bloods would try to protect their families and would probably stand up for other Muggles as well, tell people they are just as much human as everyone else; that there are good and bad Muggles just as there are good and bad wizards. Frankly, I can't see anyone close to Harry going on a full-blown Muggle-killing spree; it is, after all, something they fought against.