Easy. Put the vermin in the electric chair and turn n the switch already.
Guillotine is the only way to be sure. It’s 100% guaranteed and there is no time for the convict to experience pain.
The only reason I can think of a the reason why the left is against the death penalty, like everything else, it has to do with emotion. The walk to the death chamber, the strapping in, the last right. All of this takes an emotional toll on the convict.
We have to be more humane. I would suggest, when the convict goes to sleep, pump nitrogen into the cell. Convict will never wake up.