Calculating probabilities about nearly any real world event is extremely complex. Someone who accepts the logic of your post shouldn't believe there is much value to Bayesian analysis other then allowing you to determine whether new information should cause you to increase or decrease your estimate of the probability of some event occurring.

It should be possible for someone to answer the following question: Is the probability of X occurring greater or less than Y? And if you answer enough of these questions you can basically determine the probability of X.