I honestly don't see the problem. If a gay person thinks that conversion therapy will cure him and chooses to go through it, then it is his choice. Nobody is forcing anyone to go through it.
@applejack It doesn't have to be religious. I bet some might think the would live a happier and/or healthier life if they were heterosexual. Granted, they could just not have gay sex, but maybe they want to remove any temptation. However, I don't know if any of these therapies actually work. LGBT rights advocates say they don't, but that's just them.
@xianc78 I suppose so
Best explanation for homosexuality is the genetically antagonistic theory, which would mean it is fixed
https://slate.com/technology/2008/06/a-genetic-theory-of-homosexuality.html
@xianc78 You could make the case that allowing it at all would allow "voluntary" cases to happen too
Can hardly imagine why anyone would willingly wanna do it other than self-hating religious pressure