Yes, 'an eye for an eye' is still a viable legal principle in our modern and contemporary society. While we're not out gouging eyes as often as we should be, our courts both criminal and civil are engaged in sentencing that seeks to make the victim as whole as possible. We take something of equal value (freedom, money, etc.) from the offender to do this. It's the same thing.
An "eye for an eye" is a good legal principle in that it may deter criminals and decrease crime. If someone murders someone and is convicted, they should be put to death. If someone is robbed, that person should make financial restitution. Crime will be reduced as the principle will make criminals think twice before acting.
In a sense, it's never really gone out of fashion. I think some people are interpreting the phrase a little too literally right now, though. Instead of gouging out someone's eye or cutting off their hand, we have massive financial penalties. If you hurt someone, or make them suffer, then we take an equivalent amount of money or other resources from you to make them whole again. It's the same principle, with less bloodshed.
The simplicity of 'an eye for an eye' is not a viable legal principle in contemporary society, because following this mantra, would lead to legal problems for those being a vigilante to collect the eye. An 'eye for an eye' was used when people took many of their problems on, on thier own and without having to worry about legal issues after doing it.
The 'an eye for an eye' is not a viable legal principle in contemporary society. This is an irrational way of thinking and would not hold up in our court system or it should not. When I think of 'an eye for an eye', I think of someone getting revenge from someone else. This is not a justified reason and should not be allowed in court.