The only game I'll play with strangers is L4D2. I play it every night and it's the only game for me where playing with strangers is fun because you know you MUST all work as a team, otherwise you're screwed. You can't team kill, you can't win above your teammates, you can't ditch your teammates because it's your funeral and it's in your best interest to keep them well armed and healed if only because you might need them to survive. I feel like it's a well balanced co-op.
When it comes to MMOs, I don't mind playing with strangers BUT then you run into problems like people stealing your kills or exp., ditching you, being rude or useless, etc. I agree, though. With MMOs, I like to take my time and explore every single nook. If I'm with my friends (Which is never), I know they'll be patient or non-douchey. It's not the same with strangers.
Regarding GTAV, like someone said, Trevor is immoral, not amoral. As much a dick the game paints him out to be, he still doesn't kill the man. He knows killing people is fun and, as much as he may enjoy torturing people, he knows torturing was unnecessary. It's about the message that sends to society. It makes you question whether the torture was the right thing to do and whether the government is entitled to torture people, good or bad, just to get what they want. Pretty much, does the end justify the means?