Earlier quoted context omitted.
"Neither has been proved, therefore either is equally likely" is false, and if you believed that to be the case you would be horribly calibrated in your judgements, and parent would be right to criticize it. Plausibility is of course a much lower standard, but there is still some correct level of belief; I disagree with the parent in asserting that it is clearly below "plausible" but it's a legitimate discussion.
> Neither has been proved, therefore either is equally likely" is false I didn't say that. Go back and read my post. In fact, it's the opposite. We have many trying to claim the illegitimacy of asking questions, because there is no direct evidence. The parent went so far as to ridicule those asking questions. So, it is they who are making claims about which is more likely, given a lack of evidence in either direction…
Though actually, you're close to saying it here:
"[I]t is they who are making claims about which is more likely, given a lack of evidence in either direction."
If you lack evidence in either direction, your estimate of likelihood should be at your priors. If your mental model assigns the same prior probability to assassination as to car accidents, it's likely broken.
I recommend reading through http://lesswrong.com/lw/19m/privileging_the_hypothesis