Lexicus
Deity
I'll take this up since my friend declined. I don't see it as a "perfect be the enemy of the good" argument, although I understand why you characterized it that way.... rather I see it as identifying and rejecting a "whataboutism"-based argument. It's similar to rejecting the a "if you are going to complain about Ukraine and Palestine, you have to care equally about Sudan, or Myanmar" argument.
I'd agree that "saving human lives", as a cause is going to be subject to a lot more counterpoints than, "discouraging/disincentivizing women from having extramarital sex".
It literally uses the phrase "if we can't be perfect".
Schlaufuchs' argument was not whataboutist in any case. Whataboutism specifically refers to deflecting criticism of your conduct by bringing up other things that others have done; an argument that brings up other actions taken by the same person to point out that that person is a hypocrite is a different thing (it may or may not be a tu quoque but it isn't whataboutism).