as far as i know they don't hate them they are just pissed at the way they do things. of course any bad thing they do like poisoning the water in Durotar and Org doesn't matter to Garrosh if it helps his war machine in anyway.
laughable, if the alliance wanted to help the Tauren they would have done so when they first came to Kalimdor. in WCIII the alliance did dick to help the Tauren while the orcs went out of their way to save them and give them a land to call their won. in return the Tauren greeted and treated the orcs with hospitality of which is the most gracious thing you can do for an orc. the Tauren and orcs see the good in each other not just what the ass hat Garrosh does. and that's why Baine is in the same boat as Vol'jin and Lortheron.Other than honouring their debt to Thrall, Tauren really have nothing in common with Orcs and are a far better fit in the Alliance.
---------- Post added 2013-01-29 at 09:15 PM ----------
yea. not forgetting the alliance ransacked the barrens and the Dwarves where meddling in ancient Tauren burial grounds before that. there is a reason they are still with the horde from both forces outside, and inside.