I feel that people who refuse to give a numerical prior and use protestations of ignorance (that can be cured with a 5-second google search) as an excuse to say "very low" are really engaging in motivated cognition, usually without realizing.
Whenever one says "I don't have much info so I think the probability of X is really low", one should ask oneself:
(1) Would I apply the same argument to ~X ? A "very low" prior for X implies a very high prior for ~X. Am I exploiting the framing of using X rather than ~X to engage in motivated skepticism?
(2) Has it even crossed my mind to think about how easy it might be to find the info, and if not, am I willfully clinging to ignorance in order to avoid having to give up a cherished belief?
You can apply laws of probability to intuitive notions of plausibility as well (and some informal arguments won't be valid if they violate these laws, like both X and ~X being unexpected). Specific numbers don't have to be thought up to do that.
The question that the ideas are supposed to be in response to is:
Here are links to some proposed ideas that you should vote for, assuming you agree with them. You do have to register to vote, but the email confirmation arrives right away and it shouldn't take much more than two minutes of your time altogether. Why should you do this? The top voted ideas from this request for ideas will be seen by some of the top policy recommendation makers in the USA. They probably won't do anything like immediately convene a presidential panel on AGI, but we are letting them know that these things are really important.
Research the primary cause of degenerative diseases: aging / biological senescence
Explore proposals for sustaining the economy despite ubiquitous automation
Establish a Permanent Panel or Program to Address Global Catastrophic Risks, Including AGI
Does anyone have any other ideas? Feel free to submit them directly to ideascale, but it may be a better idea to first post them in the comments of this post for discussion.