I believe the PTC actually doesn't claim to be against depictions of homosexuality, per se (for example, their review of Modern Family refers to Mitch and Cam as "proud parents", and it's not cited as a negative), just depictions of visceral sexuality, particularly involving teens, on network TV (and early in the night, especially). It's part of their claim to be a nonpartisan organization.
Now, since the PTC consists almost entirely of ultraconservatives, most of its membership probably wouldn't mind gays not being on TV all the same. Certainly, it's founder, L. Brent Bozell III (I laugh every time I say that name), is no friend of the gay community.