Its due to the rise of identity politics. If you like cheetos, and I say cheetos are bad, if liking cheetos is how you see yourself as a person, then it could seem like I'm saying "you are bad (for liking cheetos)". It's more nuanced than that, but the gist is that non-positive thoughts about an identity category could feel like personal attacks to the people who have integrated that identity category with their sense of self.