I'd disagree with "You don't have to partake in it", and I guess that's what most people complain about. You go about, minding your own business, and then you die.
I've probably been killed about 3 or 4 times by people who were civil, and to be fair, I didn't mind so much in these cases. The other times, it's probably a 50%-50% split between "An encounter loads and you're already dead before the scene has even loaded" and "You're fighting against some NPCs and suddenly you're blown up by a rocket / shot to pieces from somewhere for no reason".
I think the main problem I have with it personally, is there's rarely any "fight" in it. It's not often like an epic and exciting battle between two players, with shots going back and forth, with tactics and skill, until one eventually dies and the other escapes with heavy wounds. It most often seems (from my perspective at least) to be a sniper or rocket launcher kills the other person in one shot, normally before they're even aware of any opposition.
Rather than it feeling like a game mechanic of player combat, it feels much more like the equivalent of a game suddenly crashing with an error, and you have to reload an old save from half an hour ago and redo everything again.
To be fair, I think I've had
one good PVP battle, when I was quite new. Both myself and the opposition had Desert Eagles or something similar, like low level stuff, probably with leather jackets or leather armour. We were probably of a similar level, and I was collecting some Gecko skins after killing them. He arrived and wanted to fight over the loot. We shot each other a few times, I crippled his legs, thought I had the upper hand... then my gun deteriorated to broken, so I tried to outrun him, and he got a beautiful lucky long range shot in my head and I died. That was actually really good fun. I didn't mind it, because there was actually something of a fight in it. It was exciting.
I can't speak about town control, or gang vs gang warfare or anything, as I've never done either. I'm a fairly casual player. It's just a shame that I've had about one of those good battles, compared to so many of the surprise insta-deaths.
[edit] That cartoon above probably says it better than I did