There can be no civilisation without the truth

The nature of the proof by contradiction (to establish a fact... or even guilt) is that we take a claim which we seek to justify (an accusation) and make the opposite appear absurd. We show that anything other than the claim we are making is absurd (nothing else could be true) and that anyone who refutes our claim is not being reasonable. They are not being reasonable to deny our claim (evidence) and we show by extension into absurdity how unreasonable they are being. For example the evidence in favour of Darwinian evolution being a plausible explanation for the diversity of life is so overwhelming that to deny it is to be unreasonable. We can also consider the juror who denies even the most profound evidence against someone who is accused. We might have photographic or even video evidence of the crime but someone might still deny it... in this case they are being unreasonable and absurd. And this is the problem with living with other people on whom your safety depends. If other people will not agree that crimes have been committed it becomes impossible to protect yourself and the community from crime. If nothing is ever true there can never be a positive conviction and criminals will walk free. Civilisation requires that sometimes people are guilty of crimes if they steal (crimes are real) and so civilisation requires some things to be true and for the rest of the population to be reasonable.