[echoangle]

I think the point frellus made was that you shouldn’t be allowed to create reasonable doubt by bringing up something you know is not true/relevant. If the lawyer know no mouthwash was involved, it shouldn’t be allowed to use the ambiguity created by mouthwash to discredit the measurement. At least that’s how I understood it.

[lolinder]

I agree that's what they meant, but why not?

The standard of proof isn't "beyond the doubt of my own lawyer", the standard of proof is "beyond a reasonable doubt". The entire job of a defense attorney is to cast reasonable doubt on the prosecution's evidence. If there's a reasonable explanation for the prosecution's evidence that doesn't involve the defendant being guilty, that's a reasonable doubt. Whether the defense attorney knows the doubt isn't true in this case is irrelevant to the question of whether it's a reasonable doubt.

Our system is designed to try to avoid putting innocent people in jail even if that means failing to convict some guilty people. It's already imperfect at that goal. We already convict the innocent. OP's proposal would tie defense attorneys' hands in ways that would lead to even more innocent people in prison.

[lesuorac]

But the defense can spend literally weeks bringing up random stuff that is irrelevant to the case that will cast doubt.

See the OJ criminal vs civil trial.

In the criminal trial the lawyers spent days bringing up every time the LA lab mishandled evidence. The LA police lab didn't handle the evidence in the OJ case. In the civil trial they weren't allowed to bring any of that up.