I think one of the biggest problems is the sheer amount of Americentricism in places like Tumblr. It's a point I've seen brought up before, like during that kimono wearing art exhibit; what nationals might find inoffensive could be the opposite for Americans. This is because people in Dubai or Japan don't face the same prejudices that Japanese and Muslim Americans face while living in a white-run country like the US. Still, it doesn't help when "people living in different areas have different experiences" becomes "American and European minorities are the only ones whose opinions matter so when we say it's objectively offensive, it's objectively offensive".