Not hating on people who like and enjoy PvP games, but to me it feels like it's a good way for a developer to make a game that doesn't actually have that much substance. Lacking content? Nothing to actually do in the game? NPCs are difficult to make interesting to fight? Just have players shoot each other. It's basically content that creates itself, not to mention (if you have good matchmaking) the difficulty ramps up naturally without you having to write better enemy AI.
I just want to fight stuff alongside other people, rather than potentially making another person's day just a little worse because I shot them before they shot me, you know? Is that too much to ask?