I don’t agree. Civil rights are rights. To take off on a day that you signed up for is not a right. Not every time that someone whines do we have to give in. This is not called being sensitive, it is called being a pushover.
Again, my point is that this is part of the job, and we all knew Thanksgiving was going to happen when they took the route. Your example about your employee taking off for a wedding is not relevant therefore, because being that it is an unforeseen circumstance, I can see that it would be insensitive of you not to let them off. Thanksgiving is not an unforeseen circumstance. The ones being insensitive are the bus drivers, not the schools.