Why do we say "Two wrongs don't make a right"?

Meaning:

It is not acceptable to do a bad thing just because someone else has done it.

Background:

The expression has a great many uses as it can be used in the context of it not being okay to do wrong to someone else because they have wronged you, such as it is not right to vandalize a person's property because they have vandalized yours. It can also be used in the context of it not being acceptable to justify something because one sees others do it - for example a politician justifying his untruths because others also lie.

It could be argued that this seemingly simple expression is at the heart of civilization as a whole because a society that believes in the law of retaliation ("an eye for an eye") holds, at a legal level, that two wrongs do make a right; whereas the society that believes that, as Martin Luther King, Jr once put it, "the old law of an eye for an eye leaves everyone blind," is built on an entirely different ethical norm.

The first known citation in the USA is in a 1783 letter by Benjamin Rush: Two wrongs don't make one right: Two wrongs won't right a wrong.

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