Probably because the lyrics are motivational and could describe an oppressed person's struggles? If a guy happens to like "I Will Survive", he could be gay. Just like if a guy happens to like a really heavy metal song, he could be gay. You can make a judgement on someone's sexuality based on their taste in music if you like, but it probably isn't an accurate descriptor.
It's a powerful gay anthem because it is one. Haha. With older songs, it was almost difficult to be overt - nothing like "born this way." If a guy knows it, it doesn't mean crap. But, it does make a difference on how much and how passionate he is about it. That's kind of a sign.
I Will Survive - Gloria Gaynor I guess this could be viewed as the definitive gay anthem. Having said that a LOT of people of different orientations love this song. Here's some trivia on it: It was initially a B-side. The A-side was called "Substitute". It won the grammy for "Best Disco Recording of the Year" in 1980. The only time the award has been presented! The video was filmed in a nightclub called "Xenon". The skater's name is Sheila Reid-Pender, from the skating group "The Village Wizards". It's been covered by lots of people including CXake, Dame Shirley Bassey, R.E.M., and Diana Ross; but not Aretha Franklin.
Wow it has so much meanings, thanks guys, I've never been passionate really but I've heard it in movies a lot so I had the song saved and the only words I pays attention to were I will survive and I read its a gay anthem and thought maybe im subconsiously gay