The US has a pretty well defined notion of "protected class" since at least 1964. Like all of law, there are ambiguities and edge cases that have not been fully enumerated or explored in case law. You're acting like this is a huge nebulous concept, and displaying confusion about minorities.

People often say "minorities" when they mean "protected class." Women are not a minority, but they're a protected class. Billionaires are a minority, but they are not a protected class. Who decides what constitutes a protected class? Case law. When a suitable number of cases demonstrate harm on the basis of membership in a class, then that class may be considered for inclusion in the definition.

The definition of hate speech in Canada is quite narrow, and hinges on the definition of protected class. Progress is slow and methodical, and not the slippery slope thay you drscribe.