The End Justifies the Means

[it]

Funny, I was just thinking of that fallacy behind the obvious answer to that - "two wrongs make a right" - it always perplexed me.

Usually I can make sense of rethorics rather easily, I even adopted a general approach where it's better to explain exactly why something doesn't make sense and the logic behind the fallacy rather then call on the fallacy by name, because I noticed people who try to the fallacy as rule book lists often don't seem to fully understand them.

But that one - "two wrong's don't make a right"... It would make sense if the argument attempts to cancel out an action, if someone would attempt to say they did not kill because they killed a murderer, the fallacy would apply, but nobody ever argues that, the justification isn't a cancellation.

In any environment where one side allows themselves to be do an act but then argues that another side shouldn't on a moral ground, they are putting themselves at an advantage, often with simplistic "it's different when I do it" kind of thinking. How would the fallacy fall on the other side then? Shouldn't the legitimacy they view in their own action create a precedent for legitimacy of others committing the same action, and wouldn't judging them for doing it be hypocritical?