If we can’t be 100% sure then I think maybe we shouldn’t have potential state-sponsored murder of innocent people.

People who are a risk to normal society do need to be separated, and for that I am willing to not be 100% sure (though with plenty of chances for appeals). If we lock up someone for a crime they didn’t commit, we at least have the option to release them and potentially pay out some kind of financial settlement as a means of punishing the state for their mistakes. If you kill someone, there’s not really much of an opportunity to even try and make it right.