Creative Speculation

If there is no evidence, there is no proof; therefore, it can be neither true, nor false as the data/information doesn't exist. If your assertion was correct then the "earth is round" argument from way back would be, by persons adhering to your criteria, false. There was no evidence (by conventional ancient standards) the earth was round, but there was evidence it was flat, which, of course, was later disproved.

Sagan was very clear when he made that statement. Just because something can't be proved, doesn't mean it isn't true (or doesn't exist), it simply means there is nothing in the way of proof to claim it is true or does exist. You cannot claim something is true (or false)without proof, which is exactly what you are trying to do by saying the "default" position is something is 'false' if no proof exists. For something to be either true or false, proof has to exist, period. You cannot claim something is false because there is no proof.