I could be wrong on this, but it was my understanding that Mann was under investigation, not from the "legal system," but from Penn State University on complaints that he deliberately and intentionally fabricated climate change data. The University committee was unable to prove this---which in a university setting is critical. You cannot have legitimate free thought without the ability to make legitimate mistakes. Now, I don't think these were legitimate mistakes, but the bar of proof in an academic setting is vastly higher than in a courtroom. This is what makes the rather watered down language associated with Michael Bellesiles's fraud about guns a few years ago so astounding, that even then they ultimately said, "We think the guy fudged data." In Mann's case, they couldn't prove deliberate fudging---but that in no way suggests his data was "clean."
You forgot the sarcasm tag.
I think, however, that the ordinary standards of academia do not apply to these guys. You’re right, a lot of mathematics wouldn’t happen if you could be prosecuted for a bad proof.
But then, there are no global social consequences if I make an error in mathematics. Most (non-mathematics) academic science is full of guesswork and claims that are quickly disproven. That’s how most disciplines progress.
Not global warming. Not only do people act on whatever is pronounced, but they ignore any science that contradicts the conventional wisdom.
The bar should be higher for them.