There are at least a few male slash/yaoi fans out there, but almost all the ones I've encountered personally have been gay or bi themselves -- one of the handful of the decent FAKE writers I've recently found is male, there was a guy in the Voyager and Sentinel scene in the mid/late 90s who has a rather famous page of gay sex tips for slash writers, and most recently I've stumbled across some cute AMVs on YouTube put together by a self-described "yaoi fanboy" from Italy. (Mind you, there are plenty of other gay/bi guys who dislike the stuff because so much of it so unrealistic...but that typically seems to be more of a head-shaking reaction rather than the visceral "ewwwwww gross wrong!" you see from so many straight fanboys.)

Speaking of which, did you see the latest "Empowered" bit on scans_daily where characters are introduced to yaoi doujinshi of themselves? *chuckles*