There are plenty of good reasons not to wear a pink #. No one really needs a list of them, because "they look utterly ridiculous" should suffice. People who wear them look like complete morons, they aren't taken seriously, and that undermines their cause. Even if I were to suspend disbelief and buy into the idea that the "Women's March" was honestly about meaningful women's issues - and not just a catch-all for a collection of socialist Cause célèbres - the hats wouldn't make any sense. If women are angry that they're not being taken seriously, a piece of vagina-based headgear is not the way to turn that problem around.
So, for that reason, you might expect the organizers of next year's Women's March (yes there's going to be one) to ditch the goofy hats.