My main message is that racial profiling is unethical whether or not it is effective.

Especially in the case I cited, it is obvious that racial profiling works better than random sampling (or based only on other features). People out of an ethnic minority will always have different rates of citizenships compared to the general population. So if you pick someone from a minority group that are less likely to be citizens, your chances are higher to pick someone who doesn't have the citizenship compared to the general population of citizens.

While the principle is quite simple, I don't have any empirical knowledge and can only refer you to Google Scholar if you desire more insights ;)