Interestingly, figuring out the answers to questions of this kind, basically about prior, we are dealing with issues similar to those in elicitation of human values. In both cases, the answer is hidden in our minds, never in explicit and consistent form, with no hope of constructing a precise model that will give the answer. The only way to approximate the solution is to consider arguments for and against, consider relared situations, think, and listen to your inner voice, to intuitive response that says that it's proper to save a child, and you agree, that it's proper to assign a probability of no less that .03 to seeing red, and you agree, and that can lie to you, beware.

P.S. Keywords for Google scholar: 'utility elicitation', 'prior elicitation', 'proper scoring rules'.