I don't consider it a non-sequitur. The point is to say, the way someone presents themselves does matter, potentially influence, and does have consequence.
Imagine someone reading a nursery rhyme to children, in blood-soaked clothes. The reading material is not the issue.
It's not the only issue, but it is the issue unless something that warrants argument occurs. We have established the fact that it would be inappropriate for a person to read to children in blood soaked clothes, or with their junk hanging out - things that would be largely unacceptable just about anywhere in public - but we have not, it seems, found a good enough argument for why it would be inappropriate in this case - except, of course, for the overall issue of who and what is acceptable to whom.
Of course if you have an issue with drag queens and their acceptance, it spills over into all activities they will engage in, but if you don't, then the argument evaporates. It is true that appearance can have a consequence, but we see little evidence in this particular issue that the consequence of such an appearance is harmful, unless you consider acceptance as harmful.
If you think about it, let us imagine that we did find a valid reason to reject an activity in a library or a paid entertainment because it exposes children to harm. Those children are, to a great extent selected and protected by parents, or should be. If your reason is valid, then would it not be reasonable also to bar such people from appearing in public at all (or to allow them to be publicly ridiculed and attacked if they do appear), because the harm they cause cannot otherwise be controlled by reasonable parents in a reasonable society?
Arguments about this sort of thing tend to occur every time some existing social norm is dropped or expanded, or some once-marginalized minority moves into the main stream. The trappings of orthodox religions, gay teachers, and so forth. We have a fear that accepting something will allow it to flourish, that some imagined purity we now have will be corrupted, and that some unwanted sin will tempt people away from the good. And sure, no doubt there are limits to what we should accept. There are real crimes and real perversions that do not belong in a civil society, but when there are, we need to deal with them thoughtfully each time. We need to evaluate what really is the threat, what really is the sin, and what really is the net loss or gain from what we do.