Lol respect each other whether you're tipping them or not. Tipping a waiter is your choice, and if you don't have extra cash saying thank you is still enough.
Prof,the fact that he disagrees with you doesn’t legitimize violation of his rights. As a professed human rights lawyer, If you sympathize only with the rights of those who agree with you what credit is that to you? Even dictators sympathize with only those who love them