The thing is, nobody's asking you to use the pronoun 'they' for/about yourself. If they were, I'd see where you were coming from, but... they're not. At all. The only time rudeness comes into it is this - if somebody tells you that 'they' is their preferred word, then it would be rude of you not to use it.
This might sound a little blunt to you by the sounds of things, but I don't really know how else to phrase it. It's just nobody else's business what other people use as their pronouns. You might well think it sounds rude and impersonal, and you're entitled to that view - but obviously the person doesn't, because it's what they've chosen to be called. Their choice of word to refer to themself doesn't affect you in any way, shape or form, so... it doesn't actually matter whether you think it's rude. It's just not a factor.
I mean... put the boot on the other foot. Say you met somebody who didn't believe in gender at all, and they refused to say 'she' when referring to you because they think it's incredibly rude. Instead they'd call you 'they', so as not to be rude in their own eyes. I'm sure you wouldn't like it, right?
tl;dr Please use people's preferred pronouns regardless of what you think of them. Please, please, please. It won't make a difference to you, I swear.
I can't speak for other people, but I actually never once called you ignorant, or implied that you were, so... I'm not sure where that's come from.
If you genuinely don't understand, then of course that's fine. I mean, realistically, you don't actually need to understand the idea of non-binary genders in order to respect non-binary people. It only becomes a problem if you start to believe that because you, personally, don't understand it, then it isn't real or valid. I don't understand how the Hadron Collider works, but I still believe that it exists. I don't have to comprehend exactly how it works in order to acknowledge its existence. You just have to kind of remind yourself that you're not omniscient. You don't know everything, you don't have every experience in your head, and there are some things that exist that you're just not going to be able to empathise with. That's just how it is.
(I know the Hadron Collider thing isn't exactly transferable. It was just an easy way to explain. A more appropriate example would maybe be this: my sister has a phobia of strands of hair so strong that they make her gag if she touches one. I have absolutely no comprehension of how you could react so strongly to something so common. I don't get it at all - but the thing is, she does feel like that. It makes not one jot of difference that I can't see what's so awful about hair. She DOES have this phobia. She DOES react that way. I just have to accept that we're wired differently and that's how it is.)
The important thing is always just to respect other people. If you don't understand non-binary people and you privately think it's made up, then... Well, I disagree with you, but we won't change your mind. Nor do we really have the right to - but regardless of what you think, it doesn't hurt to use the pronouns that people ask you to use. It doesn't hurt to stop yourself from saying 'sorry, but that's bullshit' out loud. And the thing is? It really DOES hurt other people if you deliberately use the wrong pronouns, suggest somebody is 'really a female' or say that their identity is made up for attention.
And seeing as you've brought up the word ignorant, though I hadn't used it - here's what I'd call fair notice. If you continued to do those things even now that you've read all this and seen how it hurts people? Yes, that would be ignorant. It would also be inconsiderate and rude.
Ooh - and @(you need an account to see links)? I agree that it's not justifiable to get angry at somebody for not knowing what 'fae' or 'bun' or any alternate pronoun is. After all, most people have no idea that they even exist. I actually think you'd be hard-pressed to find a queer person who uses 'fae', for example, who would immediately yell at somebody for never having heard of it before. That is not something I have ever, ever seen happen; in fact, I'd go so far as to say it's something of a queer straw man invented to be introduced in discussions like this, because I've only ever seen varying degrees of patience. Admittedly some of that patience was spread quite thin, but even so!
Far more likely would be for a queer person to get angry because somebody refused to use the pronoun after it was explained to them, or called it ridiculous etc. - and that's a totally different kettle of fish. A lot of people believe in fighting fire with fire, after all...
Think I covered everything. Sorry if no :c