I simply can't view a nonblack comedian, singer, actor, cosplayer — even a Halloween reveler — appropriating or approximating "blackness" by donning blackface without wondering what is going through that person's mind.
Upon seeing it, I'm immediately compelled to devote my mental and/or emotional resources to attempting the impossible: to read that person's mind and discern intent from the available evidence. Sometimes, I can dismiss it as harmless, or find it forgivably ignorant. Or, I might conclude it's too problematic to disregard, and address it. But, to not vet it is not an option.
This vetting is not an intellectual exercise. It's a survival instinct. Because similar dehumanization by a group in power has, throughout history, contributed to an atmosphere that devalues and endangers the lives of a group subject to that power. What I'm saying is, the response to blackface should not always be "This is some racist BS" or even to take offense. Blackface is not always "blackface"; it is not inherently racist. Everything must be taken into consideration and every effort must be made to be discerning.