Why do death penalty advocates always say "if it is applied in the correct cases"

as in "if it was failure proof".

The point is that it isn't, never was, and never will be. The moment you stop looking at individual cases and start thinking about a general system that is set up, you see that in real life these systems are always flawed, subject to manipulation and the prejudices of whoever is chosen to be the person applying them, no matter how much you with that "only the obviously guilty repeated offender etc." gets hit. The point is, wether you want to grant the state the power over life and death.

So what if the occasional "right" person gets hit with that system? For every guilty person exectuded you have people that are executed for having the wrong skin color or some other bullshit reason. It impossible to prevent that. People here say they want DNA evidence. How can one be so naive to think that DNA evidence can't be "planted" as well? Would you believe the Bush administration if they said they had DNA evidence that a bunch of anti-war people were rapists? So what if the chinese government occasionally kills guilty pirates. They kill journalists and students the same way.

Edit: can you name one country that has a death penalty system that acually "works", in a sense of it not being a tool of tyranny?

One innocent person murdered by the state is too high a price.

Do we really want to be keeping company with human rights abusers like China, Iran and Saudi Arabia?