Do MMORPGs really need dungeon difficulty levels?

I don’t remember that last time I went somewhere and was asked how difficult I wanted my journey to be, but in virtual worlds, difficulty settings are becoming the norm. Games like SWTOR, WoW and the upcoming Guild Wars 2, all have dungeon difficulty settings, mainly to allow casual players the opportunity to try out all dungeons without angering hardcore players. However by doing so, at least in my opinion, it destroys player immersion into that virtual world.