In the legal system, a class may be eligible for heightened scrutiny based on several factors, one of which is immutability. Evidence indicates that in majority it is immutable even if not completely genetic (and few things are).
Actually, it’s never been proven to be immutable, though the feelings are clearly not chosen. In fact, the immutable concept has been pushed to make homosexuals a separate class of people. Yes, it’s true that the majority of homosexuals are unlikely to change. But there are many characteristics that are deep-rooted and unlikely to change. Would that raise those characteristics to the level of a civil rights issue?