I think you're misunderstanding what the White Feather Brigade stood for. They were supporters of the war, and white feathers were supposed to be a sign of cowardice. Hence pinning them on unenlisted men in an effort to shame them into joining the army and becoming human meat shields.
yes they were pacifist, used pacific methods (if they really did only put a white feather on future soldiers' jackets), and their hate was directed not at men as a species, but at the people (in this case only men) who supported the war.
One who supports a war effort, even indirectly, is hardly a pacifist. They wanted men to enlist to fight. They were not pacifists. If they'd been pacifists they'd probably have been shaming men they saw in uniform.
It never ceases to amaze me how little of feminist history many defenders of feminism are really aware of.
I'd include language such as "mansplain" and "manspread" as designed to shame. Note that they take non-gender specific behavior and focus on them as though they were only committed en masse by men. However, anyone who's ridden enough public transportation has likely also seen many instances of "pursespreading". Also, imagine how people would react if we started using the word "femsplaining" widely. Imagine people's reaction if "momsplaining" became a commonly used word. I imagine people would lose their shit and rightfully label these terms as sexist.