Dennis McGuire did not die an easy death.
After the poison was injected he was still for almost five minutes, then he gave a loud snort, as if snoring, and continued to make that sound over the next several minutes. He opened and shut his mouth several times without making a sound as his stomach rose and fell. His awareness and terror cannot be known.
Ohio, which poisoned and killed McGuire, merely says "you're not entitled to a pain-free execution."
McGuire was executed for murder and his death was part of an admittedly experimental method of lethal injection.
Death is seldom pretty. I have watched autopsy after autopsy and read of the infinite ways people can die. I've seen a couple of deaths in person. Murderers often impose unspeakable suffering - they are also surprised how hard it is to kill someone. Murder must be punished. But the death penalty is not the punishment.
The death penalty is messy. And lethal injection tries to clean up the mess. The medical appearance of lethal injection - the healer as killer - is a show to make the killing seem like something it is not; painless and simple. The trouble is death cannot be made clean, painless or simple. No amount of makeup can hide the ugliness of death.
It's likely true that lethal injection is no worse than, say, hanging. But it's no better either. And at least hanging has the dignity of not hiding what is going on - there is no euphemism when someone is hanged by the neck until dead dead dead.
The death penalty is wrong because it (sometimes) kills the innocent, is applied to racial minorities far more frequently than justified and makes the State a stone cold killer. It doesn't bring back the dead. It doesn't deter murder. And it's inherent horror cannot be hidden by a bogus show of false medical technology.