PvE is "Wuss Mode" simply because it's us against AI. They have set patterns, parameters they can't exceed, and are locked into their programming. People are not.
I'm not trying to promote PvP (I hate it myself), I just don't frankly understand why people seem to have a problem with PvE. PvP is great fun, but only when you're going against people who are just in it for the fun, and not the fact that winning is everything, and they will use every exploit, legal "cheat", and practice both of these until they're unbeatable. Then it becomes just fun for them.
Sadly, it's impossible to make a PvP environment entirely fair. There will be people who attempt to play against people of a lower skill just to stroke their e-peen when they look at their K/D ratio. I play League of Legends. There are massive skill gaps between players, a humongous learning curve, and there is next to no true balance between characters. Why do I still play it, then? Because I play it with friends, and every once in awhile we get a match that's a load of fun because we're against a group of other friends who are cool people, and treat it as merely a game. No raging, no griefing, just fun.
I think PvE is fun though. I joined WoW to play nothing but the PvE, and I completely ignored the PvP. But I will be the first to say that after you've gotten to a certain point, there's nothing left to do except PvP. :\