take the moral high ground

To claim, purport, or make it appear that one's arguments, beliefs, ideas, etc., are morally superior to those espoused by others. The senator always tries to take the moral high ground during a debate so as to shift public opinion in his favor.

take, claim, seize, etc. the moral ˈhigh ground

claim that your side of an argument is morally better than your opponents’ side; argue in a way that makes your side seem morally better: Don’t you try to take the moral high ground with me! You’re just as bad as I am!