Interesting topic. Its been on my mind lately because I have a roommate who is bi and we've talked about it and some of my (gay) friends have added their $.02 worth.
I think hate is too strong a word but there is certainly some hostility, according to my roomy, and at best some vicious humor, from gay guys when they learn he is bi-sexual. Speaking as a gay man I think this is due to the envy and resentment gays have toward heteorsexuals who display an attitude of entitlement and priviledge (backed by legal restrictions) and enjoy a sence of belonging that gay people don't have. Right or wrong, being bi seems an attemp to have one thing while denying the other. For example, some of the posts on these site have been mean, or at best unintentional, put downs of homosexuals. I ignore them but why are we an allowable target?
Envy and resentment are very negative emotions and I try to keep them out of life and I think gay folks ought to take positve action to change laws and attitudes.
But, apologizing to the people I'm going to offend, more than one gay man has told me bi-sexual men are not straight forward and honest in dealing with personal relationships. It probably not deliberate and certainly not limited to bi's but there it is.
My roomy and I, for instance, started out as a sexual liason/boy friend relationship that fell apart quickly and he moved into his own room. Yes, these things happen but it did get him into my house and my life with out the trouble and expense of finding his own place. I think he was, in his own estimation, completely honest, but it was and is very jarring to me.