Simple ways to participate in the anti western cosplayers movement :
1. Get in the anti western cosplayers circles

2. Add more likes

3. Use the hashtag #AntiWesternCosplayers
4. Take the poll "why do you hate western cosplayers?

Why do you hate western cosplayers?

Search : For example "Cosplay of the month" to see evidences of why only us Asians can Cosplay

Japanese visualization of westerners since hundreds of years ago to this day

This is just a support evidences for http://www.antiwesterncosplayers.blogspot.com/2015/06/we-asians-make-our-anime-characters.html so check that out first to know what this is all about.

In rice cooker commercials
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In official Japanese local government tourism commercials
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Toys
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Official Japanese government pamphlets
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This one is "special" because not only it is made for official Japanese goverment release but also because it is used for education purpose of Japanese.

Ukiyo-e painting
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This is dated back hundreds of years ago.

You can also make more sense about what this is about by reading http://antiwesterncosplayers.blogspot.com/2015/06/you-westerners-are-just-look-like-your.html

There are many more like that which you can see in Japanese television and market, in case you can't visit Japan then the easiest way to see more of that is just look at the internet using search engine by using keywords such as "westerners in Japanese ads".