To respect somebody’s lived experience, their identity or claimed identity is one thing. It is declaring they know who they are and are the best to decide. You give up what you think in order to put what they think first. You respect their sense of self, and that they own that. We know that each person is indeed the best one to decide who they are, what they want and who they are going to be. Some getting it wrong is irrelevant. More will get it wrong if they let others influence their sense of self.
This does not fit love your neighbour as yourself or treat others as you would like to be treated. For example, if the thought of gender assignment surgery is personally abhorrent to you and you would not perform it on another even if you could and they needed it, conflict happens. You will not be able to reach an understanding with the person who wants their gender affirmed surgically. It is a deal-breaker if you reject a person that much.
Catholicism tells you that the power of God put in you by baptism and confirmation and the eucharist is a gift so if you have this gift you want others to enjoy it too. This is incompatible with the person raised Catholic who makes the statement of faith in Allah, the Qur'an and Muhammad as the messenger of Allah and thus becomes a Muslim. Only that person knows if they are really Muslim for the faith has to be real not simulated in order to make you Islamic. Your niceness to the person will come across as trying to entice them away from Islam with some sweet treat.
A person who doesn't even know who Hubbard is and who goes to no meetings or does not have their name on any record in the Church of Scientology may self-identify as a Scientologist. To affirm a person who says they are a Scientologist seems to you to be affirming a lie and that they are asking you to be fake and go along with it for the sake of their feelings. There is nothing transactional here. One person wants to impose their feelings and ideas on you, at your expense.
It remains true though that failure to agree wholeheartedly with who a person says they are, is attacking that person.
If there is a mess, maybe it is because morality is only a tarpaulin over a heap of conflict and uncertainty. It is true that many morals are really just about control not right and wrong and not compassion or justice.
We should not validate those who have a degradation fetish and who make themselves about a God. There is a difference between somebody claiming to be an angel or god or in touch with them and keeping this private and somebody going public and wanting affirmation from everybody else.
If they claim that they must love and serve God and give themselves away to him so that following him becomes who they are we cannot affirm that. Identity should be about you not a God or anybody else. It has been noted that idiosyncratic identity cuts you off others and may lead to you accusing them of denying how you are and denying your existence if they won’t celebrate it and agree with it. Letting people tell you who they are in terms of gender etc and agreeing with them will not make the sky fall down. Bringing faith and magic into it will. There is already enough division over identities without them making an input.
To declare that you bow before something supposedly bigger than you is definitely giving it energy and time that could be given to a real person. And/or to yourself. To declare that it exists and wants love and service implies that it may be against or even punish anyone who does not respect it and do the same as you. It thus sows and fuels the wish to see those who disobey it or ignore it learn the hard way or be punished. The temptation to manipulate and control others will rule. You will even manipulate yourself. All manipulators know that yourself is the best training ground if you are going to be a manipulator.