I don't know if its a "mental illness", I think its just a choice, a preference.
When I was growing up, homosexuality wasn't nearly as glorified as it is today. Indeed, the adults warned us kids about those who would try to recruit as into the Orientation and to stay away. Educational films like Sid Davis' "Boys Beware" showed us homosexual tactics to try and get people on board for the program.
But since then, the gay community invented things like "homophobia" and preached the idea that they are the world's Sacred Cows who cannot be offended.
I would hope that at Straight Pride Parade would be an encouragement to red blooded young men who are interested in broads, that they should be proud of how they feel.
I don't know of a single gay person who "chose" to be gay. As one friend said to me "Why would anyone chose to be bullied, beat up, discriminated against, and called names all of your life?". I know of many who tried not to be gay, and failed.
Straight men and women are born that way. I don't ever recall making a choice to be straight, do you? I've seen family and friends struggle with sexual ambiguity, and I'm grateful not to have gone through it. But I have seen a vast difference in the lives of my gay friends since gay sex and marriage have been legalized. Just not have to sneak around and hide who they are, has made an enormous difference. To have gay partners have legal rights in the hospital room, and in the lives of their children when one partner passes unexpectedly has given peace and security to their family lives that straight families take for granted all of their lives.
Pride parades are LOT more family friendly than they used to be.