A) There is no claim that genders are interchangeable in this context. In fact, quite the opposite. For almost all people, gay included, gender is NOT interchangeable.
B) Same sex relationships are close enough to "normal" ones that the differences dont' matter in this context.
c) No one knows the genesis of homosexuality, or even whether all gay people are gay for the same reason. It is morally neutral to some, but not to others. but so is dancing
D) Relationships can be different in nature but still equal as a part of a class.
E) This is both true and untrue at the same time.