I'll bite one more time, because you are making a somewhat different point. In my example of cold fusion, you are correct that my opinion is irrelevant. But then, I am not passing myself off as an authority or claiming that it does matter. Perhaps the better word here than "opinion" is "belief." I hold a belief that cold fusion is very likely bunk, simply because I have read up enough on the subject enough to know that this is what the experts think. I don't expect my belief to persuade others, but I hold the belief because it is natural for me to form a belief on a subject I have read about.
But cold fusion was just an example, one where I have a belief just because I do, and it's irrelevant to anyone but myself. The fact is, we DO rely on experts for myriad things which matter a LOT in our lives, and we do so on a daily basis. I'll hire an architect and a structural engineer to design a home for my family and me, and I will rely on the structural engineer's opinion that the design is safe. I will form a belief that the structure is likely safe because that is what the expert tells me. I will do so, and risk the safety of myself and my family on that basis, because I don't have the time to get a degree in structural engineering so that I can check his work.
In another case, I may have opportunity to vote, where one candidate advocates a policy based on a certain expert assessment of a particular issue, and another candidate advocates a policy based on a different expert assessment. As a voter, it may be relevant to me if 90% of scientist's conclusions are consistent with the policy advocated by candidate x. But according to your logic, I must form my own conclusions based on my own understanding, so if this is a highly technical issue, either I go out and get a ph.d. or it's best I just not bother voting. While I'd love to be all knowing, all seeing, it just isn't the case, and I'm not going to disqualify myself from acting based on beliefs just because those beliefs are derived from the opinions of experts rather than my own expertise.
By the way, I consider this discussion both interesting and worthwhile.
- wolf