Which logically would mean you think every one who voted for Trump not first finding out what a racist, misogynistic scumbag he is, should be labelled a racist, misogynistic scumbag.
Or does your rule vary?
Who organised the march was well known ahead of time so pretending to be surprised isn't a valid defence IMO.
Regarding President Trump, my personal view is that a significant proportion of people voted for him simply because he was the Republican candidate. I don't think there is a corresponding default position for taking part in the march.
IMO anyone still supporting President Trump and the GOP is a racist misogynist on the grounds that GOP policy is both of those things - and I'd add a side order of scientifically illiterate as well.