A silencing tactic used against male feminist allies commenting on sexist incidents is to point out that an ally is not a woman and thus can't identify sexism, or is patronising women by identifying sexism and thus presuming women are weak and need help and taking care of.
It is in fact possible for intending allies to be condescending in their actions, but the mere fact of being male and speaking out against sexism is not automatically so.
This tactic is sometimes part of a double bind, in which some defenders of an action do not accept criticism from women because the women are outsiders, or too emotional, or similar, and others do not accept criticism from men, because they aren't women.
Examples
- Anonymous comment on Lefty's blog