another thought (sorry if i'm nattering... this is all too interesting and useful):

my perception of the expected reaction to the statement "what you've just said is racist" is a cessation of discussion of whatever the original question is, and a dismissal of whatever perspectives were being offered as either out of bounds or beneath consideration.

if i take ampersand's advice to heart, then the proper reaction is "oh? ok... now, back to my problem with this..."

which sort of works both ways. either "racism" is a comma, or it is a full stop, and that depends on both parties to the conversation.