People about Cosplay...
When judging whether something is cultural appropriation, ask first: is there a cultural double standard that praises the borrower while punishing those whose behaviors/styles are being borrowed from? If not, then the second test is to see if the thing being borrowed has religious/spiritual/historical significance the borrowers are disregarding or disrespecting for the sake of ‘cool’. Finally, does the act of borrowing reinforce stereotypes?
To answer your question, No. Cosplaying in the past hasn’t been used to marginalize, dehumanize, or stereotype the Japanese people. Cosplay has no major religious, political, or spiritual significance, even in Japan it is considered a commercial hobby. Cultural Appropriation is problematic because the hegemonic group (in the US case, white people) get praise for behaviors the group that they borrowed the practice from get penalized for (in this case, Japanese otaku). However, Japanese otaku have the same or superior status as American Cosplayers at US Conventions and English language internet. Japanese Otaku are not facing a double standard when compared to white otaku that favors White otaku.
There are some racists who may say white cosplayers look more like the anime/video game characters then Japanese cosplayer, but those types tend to be seen as racists and pariahs in most well-balanced cosplay communities. Most people tend to think the Japanese have very high quality cosplay.
I think cosplay is a bit of an art form. A lot of time goes into some cosplay, especially the more meticulous, detail oriented costumes. Because of that, it’s more than just “dressing up” to me. I see it no differently than movie costumes or FX makeup in terms of seriousness. Some people even make careers into it. I assume some others are able to break into other careers like acting or the aforementioned FX makeup.
It’s not everyone’s cup of tea… and I respect that. However, there’s a lot more that goes into cosplay than what people see at face value.
What is the appeal of acting, and even role playing for that matter? Cosplay is firstly an opportunity to completely put yourself into the character’s shoes, act out a role. Additionally it is a way to showcase your craftsmanship. Just because you view something as juvenile doesn’t make it unappealing. You should be criticizing community theatre if you have that view.
Personally I feel that cosplay gives an opportunity to also put aside your own shortcomings and be someone else for the day. I feel exceedingly confident and friendly in a costume and when I see someone else in a costume, I can “know” who they are and be recognized myself. There’s a level of comradery and confidence in it. Hope that helps.