False convictions are much easier to stomach for the public when the punishment isn't final, irreversible and impossible to compensate.

The rate of such false convictions is just too high. This study estimates it at over 4%: https://www.pnas.org/doi/10.1073/pnas.1306417111

You can't be killing people for justice when 1 in 25 are statistically innocent, that's just not gonna fly anymore.