I don't need to cite any legal proof. For one thing it's not my department, and second, this is a privately owned website that facilitates the sale of goods by other people. Feel free to disagree with me about the meaning of the word "marketplace".
I will, however, cite from our community guidelines:
Do not create posts about sensitive topics that may instigate argument
While we certainly respect free speech, we ask for your consideration of others
in the channel and in our community. Avoid posting material that promotes
polarizing views about religion, race, gender, politics, or any other groups.
As for most countries not having hate speech laws, Wikipedia seems to disagree. I can assure you that most if not all European countries do; it seems I was wrong about the United States. Even so, our community guidelines cover this area nicely. The owners of Itch.io are within their rights to set such rules and enforce them, just as the owners of a mall could kick you out for intimidating or insulting other shoppers, or for that matter other sellers. We want as many people as possible to feel welcome here, and that excludes certain behaviors.