People aren't afraid of punishment. Killing inmates will have little to no affect on violence. Texas executes more people than any other state...does it curb violence? No. I'd think if any crowd were savvy to the fact that laws can't prevent violence it would be this one. Gang members aren't going to suddenly have a change of heart over the whole gang thing because of the risk of worse punishment....puleeze.
Laws themselves don't curb crime, I agree, however punishment does deter crime. In Singapore if you are caught doing any violent crime you are killed. They in fact have a very low violent crime rate (no repeat offenders).