I'm always curious whether these mistakes are intentional or not. I said "most". I was being partially hyperbolic (I honestly don't know if it's half or not, it depends on what conversation you observe really).
> they even do things like use them in debates about ways to improve our healthcare, for example
That's another commonality you will in public discussions: depending on the topic of conversation, cultures/genders are sometimes considered unique and sometimes not, by the same person. Their opinion changes depending on the topic of discussion. You see it online, you see it in the news, you see it in debates (online and real world).
If a politically correct person just came back from an overseas holiday, they will speak of the "richness" of the culture there, how they do some things in a different and often better way. (I agree with this perspective.)
The very same person, on the topic of immigration, will insist in complete seriousness, that there is no noteworthy cultural difference. Oh but also, we absolutely must have more immigration, because it increases diversity (despite the people not actually being different), which is good.
And I suppose it's necessary for me to explicitly point out: not all people do this, only some people.
Saying that [a group of] people think all people, globally, are the same is really ridiculous. Maybe online it might seem that way but people in real life don’t.