In my experience, the “racist person vs. racist behavior” distinction is not enough to prevent flame wars.
On our forum, we have a policy against publicly arguing about civility which I recommend that every Discourse forum adopt:
Don’t argue about civility on public channels. Don’t defend yourself, don’t defend others, and don’t pile on to someone who made a mistake. If you see a problem, flag it; don’t reply.
But this then puts the onus on the moderators to engage with individual posters. They (we) can then discuss the problem with the poster over PM, where, if the flames get strong, at least the fire is contained. In those conversations we usually try to grant the benefit of the doubt (unconscious bias vs. conscious chauvinism/supremecism).