To make a long story short I studied psychology and worked in the field for several years before going back to school for Networking and Security. I have friends and family in the field of psychology who are doing everything from long-term studies, case studies, counseling etc. If you really want the long version let me know.
Anyway so here is what I know; most console multi-player games are very much PvP focused, Call of Duty, Battlefield, Halo even Madden etc pit human against human. The largest video game player base is males ranging from ages 12 - 24.
Interestingly enough there have been a number of studies over the past decade following the theory of; it is now taking our youth longer to mature (mentally and emotionally) because we expect everyone to go to college. As more and more people enter college those years are being seen as an extension of ones youth. So you really aren't considered "grown up" until you are out of college.
There are more and more people waiting until their 30's to get married and even till their 40's to have kids. You know, all of the precieved "adult, settling down" things.
Where I currently work deals only with youth and I can tell you after working with kids for 7 years that most adolescent boys first reaction to any opinion that differs from theirs, or some one who is different than them is to lash out. Their arguments (as in bullet points of a debate) are more likely to focus on name calling and drawing attention to the weaknesses in their opponent/target. They are more likely to try to persuade you to understand their point of view than they are to attempt to understand yours.
So my theory is that the PvP player base tends to be those young boys making the jump from console games to PC MMO's and they are looking for some familiar game content, pvp is that familiar teritory. The PvE community tends to be more of the grown ups, those of us who grew up with Super Mario Bothers, Metal Gear, Sonic, Mega Man etc.
I meet many more folks between the ages of 30 and 60 in PvE and I meet a lot of teenagers and folks in their early to mid 20's in PvP.
There are plenty of jerks in the PVE world and there are some cool people in the PvP community. I think the jerks, d-bags, etc are actually the minority, but they are so outspoken and so arrogant that it feels like they are the majority.
No matter what,
Wheatons Law should be required reading for all MMO players. I don't always do a good job of this myself, but I try, which is more than some people can say.