People about Cosplay...
Putting aside for the moment that the tone of the question doesn’t imply the most open of minds, cosplay is – simply – acting. Do you consider Mel Gibson, Ken Branagh, David Tennant, Cumberbatch, et. al. immature for wanting to dress up and act as Hamlet? Cosplay is a similar – if not identical – mindset: people, inspired by characters, possessing the right combination of talent, bravery and self-awareness, performing as said character for an audience. Whether it’s a convention stage or a Broadway stage makes no difference. The person who portrays Deadpool or Master Chief is very much spiritual kin to the person who plays King Lear or Hamlet. It’s wrong to praise one and denigrate the other based on the source of their inspiration, for to declare which works are “great” and which are not is subjective or worse. Still, even if most consider it blasphemy to compare Marvel to Shakespeare, the motivation to portray characters from either realm is identical and the healthy mindset WON’T criticize this, realizing that whatever it doesn’t “get” is not automatically inferior or invalid.
PS: Ironically you will find, if you but ask, that most cosplayers as children were very successful Trick or Treaters, as Halloween is quite often the “bug” that bites them for their subsequent motivation.
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 actually role play as well. Role play and cosplay are almost the same thing. The only really different thing is that we not only act like the characters but we dress like them as well. The definition I give people when they ask what cosplay is, is this; cosplay means costume role play. We find a character that like/love and use cosplay as a way to bring them into the real world as best we can.
The appeal of cosplay for me is being able to create these amazing things using my skills that I have cultivated over the years. I guess it’s the same for people that like to cook. Cooking is fun and fine but I don’t think I’d really want to try my hand at making something worthy of a 5 star restaurant. That would just be way out of my skill level and I wouldn’t enjoy myself at all.
So yes, cosplay is kind of almost like that 5 star thing that people put a lot of time and effort into because they are passionate about it. Cosplay has also made it so that I have something to connect to people with. A lot of my family viewed it the same way as you do. Just adults and older teens that are dressing up on days other than Halloween. But after they saw just how much time and effort I put into these cosplays that I make they have gained a bit of a more ‘healthy’ respect for it.
If you get to know a cosplayer you will probably find that they are pretty passionate about their so called ‘hobby’. You could meet a cosplayer that may not have all of the resources that more ‘experienced’ cosplayers have. They may just sew everything by hand because they don’t have a sewing machine and work on cosplays in the corner of their shared bedroom because there’s just not enough space. Or you could meet a cosplayer that has years of experience and has won awards for their cosplays. They know exactly what kind of fabric to use for which kind of cosplay pieces. They have an entire workshop just for cosplay crafting.
But in the end we are all just a bunch of passionate nerds trying to bring our waifus and bishi boys into the real world. You don’t have to get the appeal of cosplay, just maybe respect those that do. I hope that helped you. :)