That's the opposite of what we should do. If you do case by case then people will always find reasons why it's no big deal if "their" side did it while it's really bad when the other side did it.

No, we need to universally condemn this. No matter who did it and when and how. This is lying and propaganda, and it's bad even if I agree with the ends. But the means are to be condemned by everybody.

Kind of the dual to "I disagree with what you are saying but I'll fight for your right to say it." It's now "I agree with what you are trying to achieve but I'll fight against the way in which you are trying to achieve it."