Despite your childish, closed-minded, and patronising attitude of "I don't like doing X, therefore it's crap", I completely agree with the last paragraph on PK. There should definitely be an option on game creation to allow PK, so that people who like (or don't mind) that style of gameplay can do it, while allowing those that don't want to to PVE in (relative) peace.
As for the reason people like to play PVE. It's probably the same reason why some people still play games like Mario or Zelda (I'm talking the original ones, not the crappy newer versions with shiny graphics and all that, although you could apply it to that generation of gamers, too) - it's simply what some people find fun, like going for a run and trying to beat your personal best, or reading a book. Some people just aren't competitive by nature, or don't feel that computer games are an arena where competition needs to exist for them.
I think people like PvE for the progression, slowly making their characters stronger and stronger. Atleast that's why I've always played RPG's.