I think Gay males not being as accepted comes more from the male sexual drive that any stereotype about gay males. It is my impression that men are far more interested in having two females in bed than women are interested in having two men. Therefore lesbians are viewed as interesting by straight men. (And a few men probably think that all a lesbian needs is the right "stud" to show them how great having a man is.) Women are more accepting of gay males than are men, but they tend not to be as vocal about this.
The other part of this is the idea that masculinity means not having any stereotypical feminine qualities. Therefore anyone who would submit to doing something as unmanly as fellatio or being the bottom is unmanly. They are doing it because they can't get women. So unless you want to be seen as un-masculine you cannot be gay, stereotypically. (Though even in the gay community guys that act feminine are looked down upon.)
I want to apoligize for basically duplicating klash's write up. I saw the node before any other write ups were added. Also I think this write up has more than enough votes for it, as I write this it stands at 20, and remains very high in my top nine as of AD 2001 April 13th. I'll change this notice if it drops under 12, which I highly doubt.