This was submitted to me and I have no way to reply on mobile, but I don’t want them to think that they were overlooked.
I agree with a lot of your points, and I think the way a lot of headcanons are worded makes it seem like Muggleborns are a hive mind. But of course, Muggleborns will be diverse and not everyone will like the same memes or fandoms.
I don’t think Purebloods would be shocked at the horror of scary films, but probably surprised like, “how can they show that without magic? Is that man really getting sliced open?” because the Wizarding World is very ignorant about Muggle technology and probably would need special effects explained to them.
It’s shown in the books that wizards hardly pay attention to Muggle culture, and even the Weasleys, with Arthur obsessing over Muggles, aren’t aware of how the Muggle world works. Ron shouted into a telephone in the second book because he wasn’t sure if Harry could hear him, and wondered “if he used enough stamps”.
So I don’t think it’s racism, I think wizards are too wrapped up in their own society to know about ours in much detail.