“An eye for an eye, a tooth for a tooth” is not a principle of punishment that works when generalised. Consider the case where someone kills the rest of your family. By that principle, you should have the right to kill his family, which is absolutely wrong if you consider them as independent people, and that they are not responsible for the actions of their relative, as most people do.
Consider either, someone who needs good vision to work well—say, a graphic designer—who injures someone who doesn’t, let’s imagine a singer who can already read braille through some accident of upbringing. If our singer blinds the graphic designer in retaliation to the graphic designer blinding her, then her action has greater consequences for the graphic designers life than the action of the designer had for hers, and so the retaliation is not proportional.
So, given that’s the case, how should people be punished for breaking our moral codes? Some degree of proportionality is important; murder is considered more grave than is breaking a window, the systematic defrauding of thousands of people should carry a higher penalty than shoplifting.
But again, here, how strong a given sanction effectively is will vary with the individual. If you’ve inherited millions, then you can better afford to pay a speeding ticket than can someone on the average industrial wage with no other source of funding. Does society consider a playboy driving his SLK too fast as a lesser offence against its shared beliefs than a delivery van driver barrelling down the motorway in his Transit? It shouldn’t; so fines should take into account the funds available to the offender, as happens in Finland. (Cf. http://news.bbc.co.uk/1/hi/business/3477285.stm )
Let’s consider murder, mass murder, and the death penalty.