Well, the valid argument is that we don't get to decide when and what pronouns to respect. There doesn't need to be any other rationale. It is definitely more difficult to parse than "I", but that's a matter of practicality, not validity.

You either respect the person's pronouns, explain that you have enough difficulty using them that it would be prohibitive (like I have elsewhere in other conversations) and be nice about it, or you choose to disrespect the pronoun choices. It is every individuals choice whether or not to respect pronoun choices, but the hard truth is that when the choice is based on lack of respect, it just makes the person choosing a jerk.

The use of person-independent neopronouns is a very difficult thing to adapt to. If you scan over my comments in this thread, you'll likely notice that I don't really use drag much because I have multiple barriers to communicating effectively while trying to use it. Which, I've discussed with them, and reached an understanding that it isn't about rejecting their pronoun and isn't meant as disrespect.

I do usually manage to not use pronouns at all in most cases when discussing DR's pronoun with them, and sometimes when discussing it with others like this. It's harder than just writing with the built up language patterns I already have, but easier than trying to substitute a different word entirely.

But those person-independent pronouns do have a point. The role they play in shifting how we think of gender, pronoun usage, and language in general is certainly absolutely a linguistically applicable idea. PI pronouns don't always conform to standard grammar, at least not in English, but they don't have to, to be valid as a personal expression or for the study of language.

A PI pronoun serves a similar role to other neopronouns. We do already have the singular "they/them" that are gender neutral, so neopronouns aren't absolutely necessary in the sense that other options already exist. But, if you look at it from the perspective of questioning gendered language as a whole, or from the perspective of wanting a shift entirely away from gendered language in English entirely, neopronouns start becoming much more interesting as a phenomenon.