I would advise, in most cases, against using non-numerical procedures to create what appear to be numerical probabilities. Numbers should come from numbers.

I very much disagree with this quote, and much of the rest of the post. Most of our reasoning about social stuff does not start from concrete numbers, so this rule would forbid my giving numbers to most of what I reason about. I say go ahead and pick a number out of the air, but then be very willing to revise it upon the slightest evidence that it doesn't fit will with your other numbers. It is anchoring that is the biggest problem. Being forced to pick numbers can be a great and powerful discipline to help you find and eliminate errors in your reasoning.