The issue he is that you cant discriminate on the basis of disability. That means in fairness you possibly can warn in advance without risking that.
Whilst it was possible that he would have a racist tic, it's also possible he wouldn't. That is an issue.
He was actually gracious enough to allow others to be warned (and under the circumstances he Tourettes isn't a secret) about the possibility but I suspect that actually legally he has a right for his privacy about a medical condition. However in other circumstances actually he wouldn't have to and equally if it's in the street it's irrelevant anyway.
You have to keep in mind that someone with Tourettes doesn't always tic too. So in declaring some has Tourettes and may have racist tics you are opening them up for discrimination over something that might not actually happen too.
Whilst I do get your point (despite your determination to make out I'm being a twat to black people) I'm actually being conscious of the law and what is actually practical and possible in every day circumstances.
It still remains the case that unless you think people who may have tics have to be locked up or immediately leave a situation it they do (which might put them at significant risk) or never go to certain places. Which clearly isn't ok.
Again it comes back to intent and making people understand that behaviour isn't reflective of racism and thus cannot be treated as such. This it is classed as a lower form of harm that if the same word is used in hate when assessing how you deal with a situation. This might not be how an individual might respond to the situation but legally it's likely this is the situation.
It would be interesting if you ever had a situation which went to court... Would you bring a court case in this area? And if you did what would be the outcome you would be looking for? It's be interesting to think about it in these terms as a thought experiment.
I will leave you to ponder. I am not looking for an answer to this question btw. Just asking you to ponder the point.
I personally think JD actually did and has given a 'fair amount of ground' that I suspect legally he possibly doesn't have to and that technically an employer or an organiser couldnt legally expect and ask from him as a result in the absence of an event having yet occurred. But I doubt few will even appreciate or acknowledge the situation from this position because they assume that the neutral starting point is that everyone had to be told because of their rights. I actually think the position would be in a workplace, that it's rather more complex... I don't know what the employment rate is for people with Tourettes with coprolalia but I suspect it ain't great to begin.