That is the same argument with homosexuality.
I would say there's more evidence to suggest that homosexuality is biological and not specifically an illness. Yes, it was historically seen as one, but there's a major difference between just preferring your own sex vs. wanting to transform your body.
Transgenderism has more in common with things like Body Integrity Disorder. Granted, I won't be surprised if the left tries to enable those people in the future as well.
