Besides it being a cheap knock-off of Steam, which is no reason to hate it, but is a reason not to want to use it, the reason I actually hate it is the brand segregation. I would have welcomed an honest competitor of steam, but in my eyes, if you want to compete with Steam, offer more/different features, or cheaper prices. Don't force me to use your cheap knock-off if I want to play a certain game. And although I do understand their reasons for only distributing EA games through Origin, it is ridiculous that I have ME1 and ME2 on Steam, but have to have Origin installed to play ME3!
In my opinion Origin should prove that it is a worthy competitor to steam, and worthy of space on my pc, by being better, cheaper, or by offering features Steam doesn't. Not by artificially creating a necessity of having it on your pc just to play one or two games. It wouldn't even bother me as much if all EA games were cheaper on Origin than on Steam, that's ok by me, but just give me the choice.