"The criterion he used was to have them watch a clip which was purely gay sex but in which a woman pops up in a nonsexual way. For a majority of the viewers the woman was irrelevant to their enjoyment. But there was a sizable minority who felt she completely ruined the clip for them."

This is particularity interesting. I've seen a bit of both. Porn aside, there is an element of misogamy among some gay men. Other gay men adore women and want to be one of them. As it relates to porn, when SubbyHubby was shooting hardcore cuckolding and "Forced" bi scenes, usually everyone was having a blast. It was more like tri sexual scenes than anything else. For the most part, the attitude among the people we shot with was, "Is it sexual? Then let's do it. Girl, boy, whatever." Once we shot with a gay man who was horrified at getting close to a vagina. "I haven't been that close to one of those things since birth!" He was pretty distraught, off camera. After that we made sure to vet the paid talent that agents sent to us.