There are two types of major rock stars in the world: 1) those who are beholden to the blues, traditional forms, and musicality for music's sake. This type is epitomized by somebody like Eric Clapton. Then, there is 2) those who are performers and spirit-raisers, particularly those of the post-punk generation. This type is epitomized by Bono or Gavin Friday or Morrissey or Michael Stipe.
In my experience, the two types don't get along. For example, my dad is the first type, and he also thinks Bono is an arrogant prick. And he's never heard a U2 album. It's not a generational/age thing, it's just two different perspectives.
Although I've always been a huge U2 fan, I can understand the U2-haters at times (not the mindless "Bono is a douche!" ones, but the more intelligent variety). U2 can be a bit boring, bit self-important, and of course Bono's endless sermons on stage are easy to mock and parody -- I don't think there's any doubt that even his bandmates have criticized him for this at times. You know, there's the attitude -- quite understandable -- which is: "we're here for a concert, so shut up and play the songs." I sometimes feel that way, too.
There are two other factors I'll mention for why a lot of people hate Bono:
1) U2 have been the world' biggest group for at least 22 years -- this is not comparable to any other group, and so they are the biggest and easiest target of casual music fans -- and Bono is the face of U2.
2) U2 -- and esp. Bono -- are thoroughly uncool. They themselves know this and celebrate it almost, but I think, to a lot of casual music fans, U2's nerdiness (which endears itself to fans of other bands) turns people off. U2 is almost too willing to stick its collective neck out, in the hopes that critics will chop it off (which they do). Yet, despite this fact, U2 stays big and keeps getting bigger and bigger.... which just fuels their detractors' fire.