In the US, criminal trials have a higher bar (beyond a reasonable doubt) than civil trials (preponderance of the evidence).

For executions there are additional things as well beyond the regular criminal trial.

And we get guilt wrong in criminal trials all the time (see the number of people the Innocence Project has gotten off of death row because the person didn't do it). A jury saying one thing doesn't make it objective truth.

The overwhelming majority of convicted criminals really did the deed. The existence of black swans doesn’t mean most aren’t white.

Roughly 90% accuracy. And the burden of proof is lower in civil cases.

Which isn't to say that a civil trial verdict isn't accurate to some extent - it just isn't absolute proof. There's some evidence in scientific literature about roundup's carcinogenicity at high doses (like what a farmer or landscaper would commonly encounter) and other various health issues at high dose. The big question is what happens at low doses and if it's impactful. The science is still out on that (and the alternative of lower agricultural output per unit of land area isn't really palatable from both a starvation risk perspective and a climate perspective).

No we don't. In criminal law the burden of proof is "beyond reasonable doubt". The bar is set much lower in civil law with the plaintiff only needing to demonstrate a "preponderance of evidence".