The saying, “An eye for an eye would leave the whole world blind” has good, genuine intentions to help society. It does not necessarily ring true because the “taking” of an eye would stop when the wrongdoer has been “eyed” by the victim. It would occur in sets of two people: one wrongdoer and one victim. There would not be a continuous “taking” of eyes because each person would need to be even with the wrongdoer. For example, if a man A kills man B’s brother, that counts as his “taking” of an eye. Then, to even things out, man B kills man A’s brother (or other family member) as his “taking” of an eye. Both man A and man B would be even. Of course man A, as foolish and irrational as many men are, would then try to “take” another eye, i.e., do another evil against man B. This is where the saying comes in handy. The wrongdoing must come to a natural stop. The natural stop being when both men have lost one single thing or have had something done to them, at the victim’s choice.
I much rather prefer the original saying of “an eye for an eye and a tooth for a tooth” from Exodus 21:23–27 in the Torah. This would allow many faithful people to follow the religious law and still be able to cope with the idea that God will not stop people from hurting one another because of his gift of free will. This way, the matter comes into our own hands and we can resolve it and seek fairness in having the other suffer as we have suffered. After all, why should they not suffer the same way? I know many people will shrug this off or disregard it as pure vengeance, but when this person ends up being the victim and something so dear and close to them has been taken, they may understand what it is like to be on the losing side of the fight. It’s easy to underestimate feelings and actions until you are in that situation. Empathy can only go so far, and is itself a very rare quality in people. Very few people will actually suffer when something terrible happens to someone and they cannot relate to it.
It is a very peaceful and well-intended proverb, and I more than most love the idea of peace instead of war. But, I can’t help but reiterate that our need for logic and truth should be more powerful than our need for happiness.

I beg to differ. Revenge only leaves the original wrong doer wanting revenge for that act. Cyclical revenge that only intensifies. Gandhi’s non-violent ways (where the leave the whole world blind phrase comes from) is a great example of turning a wrongdoers action against them without striking them back. Jesus took much the same stance in Matthew 5:38–39: You have heard that it was said, “An eye for an eye and a tooth for a tooth.” But I tell you, do not resist an evil person.
I appreciate your pondering over phrases we hear every day.
Peace be with you.