I just don't like it when people accuse others of being gay because they don't support gay rights/hate gay people and are very vocal about their opinions. It doesn't make any sense to me.
I'll try to explain it then, but first, the environment has changed so much for the better for gay people that I don't think it's nearly as common as it has been even in fairly recent history. It's less common in the younger generations in particular.
See, take a particularly uncomfortable taboo like homosexuality which can result in a lot of bullshit or even violence but is not overtly apparent like race and can be concealed, then there's an incentive to convince people that you're not gay. People have been known to over-compensate by being extra womanizing, at least in how they express themselves, sometimes to the point which most people would find really inappropriate, like saying the things that you whisper to your buddies about hot women but saying it right in front of her and really loudly for everyone to hear. After all, they're not really trying to impress the woman. It's a display for everyone else.
Another case is to loudly and frequently express how much you just can't stand homos. How can you possibly be one when you hate them so much, right? IT'S WRAWNG! THE LAWD SAYS SO IN TEH BIBAL!
It's not that complicated. I thought it was something pretty broadly recognized and I'm surprised this is news to you, but as I said, times are changing. Maybe that's why.
But as I said before, I'm usually quick to point out that it's an oversimplification. The same tactics can be compensation for other kinds of insecurity, though usually masculinity-related as both kinds of overcompensation are like expressions of hyper-masculinity. And yes, of course I wouldn't presume that this explains every example of said behavior. It just frequently tends to be the case. They have done studies that showed a correlation between guys expressing overt homophobia and being turned on by gay porn vs. not being homophobic and not being turned on by gay porn. I'm always leary of studies and whether they were conducted properly so I'm going more on anecdotal experience, both my own and those others have talked about.