Liberals usually claim that homosexuality is inborn. Religious people and manospherians usually claim that homosexuality is a mental illness. Both commit the same fallacy, an appeal to nature based on personal bias. Both assumptions, when declared doctrine, are potentially harmful.
If we declare that homosexuality is inborn, we take all hope away from those who truly suffer from emotional disturbances and developmental setbacks. They are left in a desperate situation and when trying to reconcile the conflicting voices in their heads, they feel forced to support the voice that urges them into homosexuality, inflicting strong pain on themselves from even thinking about it.
On the other hand, I think it is plausible to make room for the assumption that some people are truly homosexual at their core and suffer gravely from having to repress that. Telling them that homosexuality is a mental illness hurts them just as much as those who experience the dilemma from the other perspective.
To make a little analogy, there may be a man who truly enjoys photography and art. And there may be another man who truly enjoys hard work and carrying around big bricks at the building site. Now let’s assume that each of them thinks that his profession is the only true and natural thing to do for a real man. They get children. The artist’s kid would secretly love nothing more than to be a hard worker. The hard worker’s kid would love nothing more secretly than to be an artist. Let us assume that both shame their kids for not doing what they think is the right way. Both kids suffer for having to be something they do not truly wish to be, feeling guilty towards their parents for not truly wanting to be their narcissistic mirror image. And yet, the fact that the kids suffer from having to live a life that does not fit them does not mean that this life would not perfectly fit somebody else.