How should we explain the cases of those who are male or female but claim to be or want to be because they feel they should be the opposite gender?
Well, in the Bible there is no choice "C" for gender. God made them male and female. So if you want to talk strictly in terms of the raw truth, then these people are simply not in touch with the reality of their bodies. For some reason, there is a kind of animosity there in the person's mind about what they physically are, and some kind of strange or abnormal idea about what the gender is that they think they are or want to be.
For instance, a man who likes to wear woman's clothes may claim he is a woman. If you could give that man a high dose of truth serum, and rip away all of the lies human beings sometimes convince themselves of to condone the things they do that bother their conscience, and you asked the man why he thought he was or wanted to be a woman, you would probably find the focus to be (in this case) upon an unnatural pleasure of wearing womens clothing. In another case, you might find the person's father was cruel to them, while their mother was nice, and so the opposite gender has for them nice and comforting feelings associated with them, while their own has nasty, cruel implications.
In all cases, though, I bet you'd find that it is grounded in an identifying with some quality they perceive in the opposite gender which they find comforting or good, and some idea of their own gender which is largely bad. They may say "oh, I have nothing against _whatever they are_, but... I just feel this way." But if they had nothing against what they were, they would not psychologically be trying to escape it.
The human mind is an incredible thing. But it will do everything it must in order to achieve optimum comfort or peace. (Partly why everybody's got a selfish streak they have to overcome.) If your mind recognizes there is a problem, or a source of mental discomfort, it will do everything in it's ability to ease or erase that problem. If a person develops in their childhood an idea that, for instance, "men are hard, cruel, unfeeling, bitter, nasty, etc..." and they are a man... and meanwhile they see women as "nice, pleasant, kind, generous, sweet, etc..." the mind is going to have to deal with that twisted view of the sexes. If the exaggeration of those traits which make up their view of the sexes isn't corrected with the reality early on, they may very well have problems with their gender. The subconscious mind is saying to itself, "Well, men are something BAD... but... wait... I'M a man! Well... I don't want to BE a man then! I want to be GOOD like women! Ok, so I'll BE a woman!" And so it proceeds to fixate on things which the person calls "being" that opposite gender.
They don't have to literally have that conversation with themselves in their head. The ɧoɱosɛҳųαƖ doesn't have to either. But at some point, they've formed the idea that a certain gender is evil in some sense (or over all), and the other is better in some sense (or over all). In order for a human being to remain sane, either the idea has to be corrected in their thinking, or else their mind will simply twist and turn itself into knots until one is finally comfortable with themselves given the ideas that they have. So the woman that decides men are evil may end up a lesbian, and the man whose father was completely either cruel or absent to them, may try to be or wish he was a woman, for examples.
The reasoning is pretty sound here, I think, but I would also add that they CANNOT ADMIT that this is the case. If they admit that their ideas are wrong, then, their mind objects, they would have to BE (or be with, in the case of ɧoɱosɛҳųαƖs) that undesirable sex. So at all costs, their subconscious mind will fight to the death rather than admit that this is the case, precisely because they DO believe the things they do about the sexes. Thus they explain it in other ways, "I was born with the wrong body" (as if God could make a mistake!) or "I was born ɧoɱosɛҳųαƖ" (as if God would make someone from their innocence to offend Him!).
There is nothing worse to either of these types of people, than to admit that their concepts of the genders, or of why they are the way they are, is wrong. Just try to challenge their delusions of what they are, and watch the bomb go off! The ɧoɱosɛҳųαƖ will NEVER admit (or at least very rarely) that they "chose to live in sin," and the person who wants to be or thinks they are the opposite gender will never admit that they "simply are the gender they are, body and soul," and that they "made the choice to be or play the other gender" because of the ideas they hold. Their explanations will always twist the reality, and excuse them from any guilt or responsibility of choice.
For that matter, alcoholics often cannot admit they are alcoholics, because along the same lines, THEY don't like the implications of the truth, that they have a problem, that they are responsible for their choices and actions, and that they need to stop their bad actions.
This is all simply my take on it though. I don't think the Church (in it's sane days) has made a pronunciation on these technicalities, so much as to condemn the actions of the people who are in that position. Sometimes it's a matter of people knowing they're doing something wrong or "sick" (since sin is not in the world's vocabulary), and choose to do it anyway because of the sheer pleasure factor, but often times I think it goes a lot deeper to, as I said above, their deepest ideas of the sexes, and the mind trying to deal with those ideas in such a way that they can live with what they are, or who they OUGHT to be with romantically (if anyone).