When you create a character, you get the option of whether you want him in pvp or pve server.
I mean there is obviously demand for it and there is obviously people that don't enjoy it, so why not give both what they want. I guaranty you that the pvp server will be just as full as the pve servers, if not more!
Whoever hates pvp, There is absolutly ZERO reason you can come up with against such a concept. If you do not wish to get hostiled or fight in such dangerous enviroment, then pve is your servers.
I believe that the reason there is no pvp in Diablo is because they have pushed away all the original diablo creators out of the company and they were probably the ones that believed in it as a core. Thus you have all this new talent working on a game with other intentions in mind.