More than rude, it's a social taboo to criticize feminism.

The social taboo against criticizing feminism is built on the taboo against male violence against women. Note how readily some people label criticism or disagreement as "harrassment" and "violence", or how women who disagree with feminism are erased from the debate -- this is how the former gets labeled as the latter.

If we succeed to reframe the situation -- if we see a man verbally disagreeing with a feminist, but our emotions correspond to "a strong man is beating a weak woman" -- then the instinct to protect the woman gets activated.

At least it is my experience that in eyes of most observers I would lose any debate with a sufficiently skilled female feminist, because she could twist even the most polite verbal disagreement as "attacking her" simply by starting to cry. People pattern-match all the time. They see a man opposing a crying woman; their brains may try to analyze what happened, but their hearts already gave a clear verdict.