If one party is espousing a hypothesis which has a very low prior probability, then they suffer the burden of providing evidence to support this hypothesis. Finding evidence takes time and resources; if you want to support the low probability hypothesis, then you spend the resources.
a hypothesis which has a very low prior probability
Its probability is different in estimates of the people who disagree, and its best alternative will find the status of having "low probability" in estimate of different people. Just "low probability" doesn't make the situation asymmetric.
if you want to support the low probability hypothesis, then you spend the resources.
You should spend the resources when there is high value of information, otherwise do something else. Improving someone else's beliefs may have high value for them.
You know the drill - If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
And, while this is an accidental exception, future open threads should start on Mondays until further notice.