I was going to say: I’m not aware of debate settling science, but I’ve seen science settle debate. But then I remembered that debate doesn’t need evidence or truth value to thrive and it often isn’t settled by science.
As far as law, I don’t know if you mean debate in a court or debate in a legislature, but I can’t imagine a good faith argument to defend either and I don’t want to strawman you.
In any case, the idea that debate is a method to discover truth value is based on the fallacy that being presented with evidence and reason is how humans form belief. Believing that evidence is persuasive is itself a denial of the overwhelming evidence to the contrary.