What is the probability that the text between the quotation marks in this paragraph is "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Fusce id velit urna, ac sollicitudin libero. Phasellus ac rutrum nisl. In volutpat scelerisque justo, non congue diam vestibulum sit amet. Donec."? The prior probability of this being true is minuscule, looking something like 10^-60; therefore, you might as well rule it out now.

Prior to what exactly? I do have a prior for "a randomly generated ascii string of that particular length being the same as the string given". I wouldn't be able to know to use that as the prior unless I have already been given some information. Then there is all the knowledge of human languages and cultural idiosyncracies I happen to have. Which of those am I allowed to consider? It's hard to tell since, well, you've alreay given me the answer. It's a bit post for any 'prior' except meta-uncertainty. I would need a specific counter-factual state of knowledge to be able to give a reasonable prior.

(All of which I believe supports your point.)