I call people by their preferred pronouns because this is something that’s completely inconsequential and meaningless to me. But the same kind of argument can be made against you: “So you’re saying taking “no” for an answer is a great difficulty for you?”
If I traveled to some country where a particular religion - let’s call it X - was the most common, and in X people were ascribed different pronouns based on some rules or rituals, I would call them by their preferred pronouns because as an atheist and moral anti-realist that’s just not something important to me. But if a Christian felt uncomfortable doing so because it goes against their religion their position is just as valid - arguably it’s more valid since in this example the people from X are asking the Christian to change their vocabulary, while the Christian isn’t asking anything of the people from X.
Some Christians feel uncomfortable treating people of another skin color as equal to them and say it’s because of their religion. I don’t really give a shit if you think your magic sky god gives you license to be rude.
You’re moving the goalpost as treating other races as equals and using different pronouns are not the same thing, but again the argument can be turned against you: Why are you rude towards Christians simply because they prefer to use a different pronoun when referring to you? Is taking “no” for an answer such a great difficulty?
To be fair, you started moving the goalposts by invoking special privilege/motivation for misaddressing people.
But to answer why I would be rude to christians for misnaming me, is because in my culture it is rude to misname people, and even more so when they’ve offered a good natured correction.
If you say you’re William, and I call you Shirley, would you defend my right to call you Shirley?
And why would it be different if The Almighty Bob said to surely call you Shirley?
Rude to Christians? They’re the ones who are saying their religion tells them that they can’t call other people what those people want to be called. That is the rude thing. How would you like it if I used a pronoun for you that was not the one you went by? You’d probably think it was rude. How about if I said it was against my religion to call you by the pronoun that fits your gender? You’d probably still think it was rude.
And it would not be rude to tell them off for doing so.
That said, in my experience, most trans and nonbinary people are incredibly patient with people like you who refuse to use their pronouns even though you’re being extremely rude to them.
First, I would ask that ‘Christian’ why they felt the need to travel to a country they felt uncomfortable using the local language in.
Also, in this scenario they would be asking for something from the people of X: The right to not use their language in their land.
I know the Christians near me have specific views on when other people should speak their language when they’re on their land.