Because it is wrong.
I am not judging sexual practices. I am judging those who choose to betray their partner. Here is the person he is most committed to in this world, the person who expects undying loyalty in exchange for the same in return, and he is seemingly shitting all over that vow.
If you only care about practicality, then consider that one will not care for the people in general if they cannot care for those closer to them. Honesty and compassion mean nothing to this man.
On the other hand, I very much appreciate knowing which celebrities support an administration that poses a threat to my family. I will not vote for someone based on a celebrity endorsement, but the celebrity may gain or lose my business over it.
I really liked Kid Rock in his early days. The music was catchy, and it had the right mix of redneck, rock, and rap to make this country boy happy. Now I won’t listen to him because he chose to openly throw in with politicians who do not care if their policies and rhetoric kill my friends or kids.