Bayesian inference is very, very often used in the types of philosophical/speculative discussions that Rationalists like instead of actual empirical study. It's a very convinient framework for speculating wildly while still maintaining a level of in-principle rationality, since, of course, you [claim that] you will update your priors if someone happens to actually study the phenomenon in question.
The reality is that reasoning breaks down almost immediately if probabilities are not almost perfectly known (to the level that we know them in, say, quantum mechanics, or poker). So applying Bayesian reasoning to something like the number of intelligent species in the galaxy ("Drake's equation"), or the relative intelligence of AI ("the Singularity") or any such subject allows you to draw any conclusion you actually wanted to draw all along, and then find premises you like to reach there.
The reality is that reasoning breaks down almost immediately if probabilities are not almost perfectly known (to the level that we know them in, say, quantum mechanics, or poker). So applying Bayesian reasoning to something like the number of intelligent species in the galaxy ("Drake's equation"), or the relative intelligence of AI ("the Singularity") or any such subject allows you to draw any conclusion you actually wanted to draw all along, and then find premises you like to reach there.