It's not a new phenomenon, people tend to hate stuff that crashes into the mainstream as Halo has done, just look at the Wii. In some peoples heads, this equation is created:
Halo sells insanely well + large cultural legacy = Everyone thinks Halo is the best game ever.
This is flatly untrue. I've never met one of these rabid fanboys (although I'm sure there are a few) but I've met dozens of trolling haters who give very flimsy reasons for disliking it.
If Halo ever dies on its arse, eventually people will hail it as the best game EVAR, then when it is resurrected they'll get accused of "milking" and be hated again. It's just how trends work.