As I recall, “Mutant, and proud” was a repeated line in the more recent movies used as a rallying cry.

Using the term as an insult is probably counterproductive given the popular media association of stories of people being oppressed for their differences.

IIRC, the X-Men was originally an allegory for the Civil Rights movement - complete with some “mutants” wanting to work within the system to improve things and others wanting to tear the entire system down.

Of course, all persecutions tend to share similar themes even if details change so the story of the X-Men is easily applied to LGBTQ folks as well as any other group that’s persecuted against.

And if someone sides with the people who persecuted the X-Men without realizing that this makes them the villains, they really are idiotic.