Edit: Seems pretty clear to me: Willamena is just saying the same thing I've been trying to say: if you're going to make a definite statement, be prepared to back it up with something more substantial than "well prove it isn't".
I didn't get that from Willamena's post at all, but okay.
If' we're going to recognize that as a legitimate tactic, anybody can get away with anything:
How's this:
"I'm King tut, prove that I'm not. If you can't then I am by default".
"2036523098560975406 light years from earth there's a planet made of milk duds inhabited my flying Smurfs. My proof? Well, prove that it isn't. You can't? Well then, I rest my case".
OK, at least now I see the appeal to this approach.
Or... "people keep on living after they die, and when they do, they inhabit an invisible, undetectable realm, and even though it and the people who live there are invisible and undetectable to us, I still know about it somehow"?
Edit - that milk-dud smurf planet: we have no evidence for or against it. Is it reasonable to presume that it doesn't exist?
If yes, then how is this different from presuming that an afterlife doesn't exist?
Edit 2: I say that there's no difference, and that it's reasonable to discount the possibility of both the milk dud planet and the invisible realm of dead-but-not-dead people on the same basis.