That's not reality: Every court case has to decide on truth. That's why we have laws, court procedure (including rules of evidence), and judges and juries. Juries specifically are tasked with deciding the facts of the case. Fraud and slander depend on determinations of truth.

It's not always simple; it's not always perfect; but practically we do it all the time as a matter of course. Everyone makes decisions like that every day; every authority makes those decisions - managers at work, politicians in hearings; the public does it listening to political messages, parents do it listening to teenagers explaining where they were all night ...