Honestly, now that Baine has actually taken action, at least he’s more consistent with his ideals than “some” characters. He’s an idealist, and as an idealist he believes in an ideal concept of the Horde, and works towards it. In instances where he feels the Horde is moving away from that ideal, he react negatively … And since he doesn’t really have any personal reason to be antagonistic with the Alliance (outside of those events caused by his people’s affiliation with the Horde) … he doesn’t seem to care if his reactions are beneficial to the Alliance or not.
Long story short, the only reason the Tauren as a whole are even part of the Horde anymore is because of him. A lot of people give him crap for his reaction to Taurajo (which essentially boiled down to building a huge wall, and being satisfied with the death of Hawthorne and his men), but they also neglect to discuss the political pressure he was under by large factions of Tauren to LEAVE the Horde (in “As Our Fathers Before Us”); where many Tauren rightfully blamed their affiliation of the Horde as the reasons for the hardships they faced under the Garrosh regime.
Bluntly, Baine shouldn’t be part of the Horde anymore (nor should most of the Tauren). In many ways, they’re culturally incompatible with what Sylvanas is turning the Horde into (which is ideologically the Forsaken). The reason they don’t leave is a combination of Baine’s belief that HIS Horde is worth fighting for, and the fact that the Tauren being landlocked on Kalimdor makes defending themselves against the Horde really difficult should they leave it. After all, they have one of the largest sources of Fresh Water the Horde depends on at their disposal; the Horde just can’t let them leave.