The reason for a constitutional amendment, according to somebody on NPR, is that it gets more broadly applied than does a statute. I personally am in favor of switching back to the compensation form of justice rather than the retribution one - the perp should have to make it right with the vic, not have to go to jail and get fed and clothed and housed and taught crime at the graduate school level. But I grew up in the Third World, where justice is still more based on reparation than retribution, so that feels more normal to me.