I was talking with a friend about self-publishing some of my romances, and she said it would be best to put out a series. I told her I had an M/F romance which was almost ready to go, except the subsequent books in the series are all M/M. I read (and write) both kinds.

She cautioned me that while a lot of readers of straight romance seem to be open to an occasional gay romance that's part of a series, it doesn't work the other way around. Then she said, "M/M readers can be virulently anti-m/f - I belong to a few reader groups on facebook and about once a month or so, someone makes a post about how they will never read an m/f book again now that they've found m/m, and a bunch of people chime in to agree."

I was wondering about this. Preferring one type of romance over another is fine, but the "virulently" part was a bit worrying. And since I enjoy both M/M and M/F romances, I'd like to know why readers might dislike M/F romances. Do the people in a gay romance seem on a more equal footing because they're both men, for instance?