An eye for an eye only ends...

"An eye for an eye only ends up making the whole world blind."
- Gandhi

If an eye for an eye mode of punishment was applied to the whole world then not everyone would become blind because not everyone is poking out other people's eyes. What that means is not every person is doing bad things to others. With an eye for an eye mode of punishment a person who commits homicide would be killed, a person who steals a sofa would have a sofa taken from them, a person who blackmails would be blackmailed. But not everyone is stealing sofas, murdering, or blackmailing!

Someone could argue that since nobody is perfect everyone would be punished to some degree. But not all bad doings can be mirrored on the doer and still be considered punishment. Let's say you insult someone, then your punishment is to be insulted...not much of a punishment or deterrence from insulting again.

And that brings up deterrence. An eye for an eye would convince many (not all) people that they shouldn't do something bad; they've been deterred before committing the crime. Those people will not be "left blind."

Not many people, myself included, would want an eye for an eye. However, current crime punishment is obviously insufficient due to many factors. People should remember that punishment should be a deterrence not a slap on the wrist. Gandhi probably would have said that it would be better to forgive the criminal than punish them, and people are entitled to that opinion, but not many people would find it morally viable to forgive a person for killing a loved one. And forgiveness wouldn't solve the problem that there's a killer on the loose anyway.