I agree with the premise, to a point. If such a concept were to become law, I could see the liberal DAs in blue states trying to convict someone of a felony in a self defense scenario just to see the original victim executed.
True, a person who commits a felony with a firearm should be heavily punished. True, the appeals process in capital cases are beyond absurd (think justice delayed is justice denied). It amazes me how readily courts can clear room on their docket when Johnny B. Scumbag is facing imminent execution for the murder he was convicted of 20 years ago.
I agree, use of a gun while committing a felony should be heavily punished. Not confident that a mandatory death sentence would be used to further justice as one would hope.