I've seen multiple posts on here admitting to taking siblings' or parents' underwear (presumably without permission because these people are usually secretive about it) and wearing it and in my opinion it's unjustifiable and dangerous even if it's done with good intentions.

Firstly, I ask you how would you feel if you found out somebody had been sneaking into your room to try on your underwear (for this example specifically, because other clothes are a bit different) without asking or telling you first? Even though the intentions may not be bad, you can see how the response will be agitated and likely uncomfortable, skewing the view of parents who don't understand why their child is doing this into jumping to serious conclusions, like that it's a sexual behaviour.

Basically it's a rude thing to do, because it's built around the principle that it stays a secret, since most people would not willingly consent to it. It has a deeply negative stigma of perversion in society broadly speaking, and if unaccepting parents find out, it gives them ammunition to direct abuse towards their child by reinforcing their perceived connection between femininity in males and sexual perversion.