[jpallen]

'if X is true then I expect to see evidence of X' is generally a reasonable assumption/prior. So not seeing evidence of X is evidence that X is false. It's not proof, but absence of evidence generally is evidence of absence, unless you have a specific reason to believe it's not.

[new2628]

The specific reason is the asymmetry in being wrong in one direction vs the other. If we thought a virus does not spread in a certain way and we are wrong, we may die. If we thought the virus does spread in a certain way and we are wrong, we may unnecessarily wear a mask.