Well they have deathmatch missions if all you want to do is run/ride around and kill people. I'm glad they implemented the bad sport mechanic. I don't mind people trying to kill you or fuck with you, but some people just literally ride around the whole time trying to kill other people (they die, spawn, and then race back to the scene of the crime to try it again). My brother and me have killed the same guy over 10 times in a row who just keep coming back trying to kill you. If you want to do that, it will put you in a server with other people who want to do nothing but try and kill other people. I don't see the problem here.
You lose $2000 every time you die, and when you kill someone you may be lucky and get $200. I don't see the appeal in trying to kill other players repeatedly in an auto-aim video game. If you're out trying to rob stores and you continually have the same guy or group harassing you (instead of actually doing something productive) it gets annoying. I don't see a problem sticking people like that in the same server with other players who only want to ride around and kill others.
I like to go for people with bounties, but otherwise I generally don't fuck with other people. And killing the people is not going to give you a bad sport, it's just when you blow up their cars (I believe to discourage people from sticky bombing or grenading other people's cars, which is a pretty easy way to kill someone). You only pay like $500 if your car blows up if you have insurance. So it's no biggy.
Only problem I have with the "bad sport" thing is that if you're on a mission, you can get kicked from a server and lose reputation.