Two wrongs don't make a right: Hypocrisy on the ides of March

Moral education taught us that two wrongs don't make a right. One should never assume that if one wrong is committed, another wrong will cancel it out. One cannot justify a wrong action by pointing to another wrong action of the accuser.

Why? Doesn't the two negatives (wrongs) cancel each other out? Isn't it a mathematical fact that multiplying two negative numbers produce a positive number?  The two wrongs don't cancel out beause this isn't math.

Text book logic tell us that tu quoque is a very common fallacy in which one attempts to defend oneself or another from criticism by turning the critique back against the accuser. Tu quoque, Brute, fili mi, by the way, is what Caesar said before he was assassinated. Literally it means "you too?". Shakespeare wrote "et tu?".

However, not all tu quoque arguments are fallacious. They are also used to show inconsistency, to indirectly repeal a criticism by narrowing its scope or challenging its criteria, or to call into question the credibility of a source of knowledge.

The ever reliable Google brings us to the Wikipedia page, and I quote:

A legitimate use of the you-too version might be:
    A makes criticism P.
    A is also guilty of P.
    Therefore, the criticism is confusing because it does not reflect A's actual values or beliefs.

Example: "You say that taking a human life is wrong under all circumstances, but support killing in self-defense; you are either being inconsistent, or you believe that under some circumstances taking a human life is justified."

Immediately ascribing an argument as tu quoque may be just a ploy to hide the original wrong. If a wrong has not been tolerated early on, the succeeding wrongs might not have happened. This inconstency, or uneven and selective application of moral standards, is pure and plain hypocrisy.

Equal application of policy is akin to equal application of the law. The US Supreme Court, in a case about an unconstitutional application of the law due to violation of the guarantee of equal protection, reasoned: “Though the law itself be fair on its face and impartial in appearance, yet, if it is applied and administered by public authority with an evil eye and an unequal hand, so as practically to make unjust and illegal discrimina­tions between persons in similar circumstances, material to their rights, the denial of rights is still within the prohibition of the Constitution.”