Adding the But...

If you start a sentence to defend someone with, "I know he's a liar but...", you are defending a liar.

If you start a sentence to defend your vote with, "I know he's a bad man but...", you are defending a bad man. 

If you start a sentence to defend a flag with, "You can unfriend me if you want, but...", you are defending something that you know is wrong.

If you start a sentence to defend a point of view with, "I am not a racist, but...", you are at the least about to defend racism or at most a racist.

If a politician starts a sentence with, "I've known him/her to be a good friend, but...", he/she is about to trash his/her "good friend."

Using "but" may make you feel safer in a terrible belief, "but" it does not alter the fact that it is still a terrible belief. You are defending, attacking, protecting something that is clearly indefensible. 

There is simply no buts about it.