I'm not buying it. I'll buy that exposure to gay porn can influence someone who's already gay, but was repressing that orientation due to cultural pressures, to admit being gay. But the idea that heterosexual people are being "turned gay" by exposure to porn is utterly ridiculous. I'm reminded of a YouTube video I saw in which a conservative Christian claimed that moving from a small, rural town in the Midwestern U.S. to a large city introduced some sort of corrupting influence that caused people to "turn gay", angrily rejecting comments by those pointing out that it was simply that people who felt compelled to hide their sexual orientation due to the intolerance of their small town communities were finally freed to openly share it with a more tolerant circle of friends and acquaintances.
When I was quite young, I felt myself attracted to females long before I even had any inkling of what sex was. In discussions with friends, heterosexual, homosexual and bisexual, they've expressed the same early attraction to the gender(s) to which they are currently attracted, long before they understood anything about sex. I've yet to see any evidence that people can change their sexual orientation by willful choice or external influence. All I've ever seen is people deciding to be honest with themselves about their sexual preferences.
Lastly, I don't care if people are gay. It's nothing to be ashamed of, and they certainly don't need bigots trying to diagnose why they "turned gay" like they have some sort of disease.