I take it as self-evident and undisputed that when a group of eminent economists sign a letter endorsing the health care bill, the subtext of their message is that the issue is part of their scientific expertise and that they have studied the details sufficiently to deliver their professional opinion: This is the only way to interpret the fact that the undersigned are all economists, and that their academic position is mentioned in the letter. This is why their advice should carry more weight than the advice of an unknown blogger. If this advice is followed and the bill passes, then some of their professional reputation is tied with its success.
What is perhaps more disputable, but still true in my view, is that even this group of most distinguished economists don’t have individual reputations, and that they are drawing from and contributing to a collective reputation pool of the entire profession. The people of this (or any other) country, who are the audience of this letter, don’t distinguish between different scholars of the same discipline. Public trust in the entire profession is determined by the success of the predictions and policy advices of its members.