You can police the execution of people's racist intent, and we often do. Freedom of speech and freedom of association mean racists aren't guaranteed a platform. Many countries (not the US, notably) police "hate speech" on the premise that such speech inevitably leads to hateful actions.
Arguing from human nature isn't compelling. Rape and murder are part of human nature as well, and people have always done both, yet it isn't controversial to police such behaviors. Racism is no different. We aren't mere animals entirely beholden to our base instincts, after all.
Of course I wasn't talking about or advocating jailing people for offensive memes, but I understand this is one of those subjects Hacker News can't approach in good faith and I take the downvotes and shit-eating snark in stride.
Arguing from human nature isn't compelling. Rape and murder are part of human nature as well, and people have always done both, yet it isn't controversial to police such behaviors. Racism is no different. We aren't mere animals entirely beholden to our base instincts, after all.