The most vitriol comes from rap haters, bass haters, and haters of anything popular (audio hipster types). Of these, I can only really understand the bass haters because at least they are consistent (they'll hate on any can thats bass heavy no matter the brand) and it boils down to their personally preferences in music.
Yes, they are overpriced. Yes, there are better headphones for the money. But I don't get the outright hate. They could end up being great gateway can. Slowly, exposing people to the idea of buying better headphones priced at higher than $30. Once people have accepted that headphones can be priced in the triple digits, its not a big leap for the truly interested to go to beyerdynamics, senns, akgs, etc. Just as some iPhone users (who may initially buy their phones based on aesthetics) eventually turn into power users who see the light and switch to more viable platforms. Beats is growing the > $150 headphone market which is a VERY GOOD THING. Now its up to other manufacturers to step up and make cans that can start chipping away at Beats' market share and a lot of them are trying, they just haven't struck gold yet.