For pure scientific debates, I'm all for inviting any scientist with some amount of credentials to the table.
But for public policy debates, I think the track record is exactly the opposite: for every major public policy issue that required scientific knowledge, inviting the reactionary types dug out by the sleazy PR industry has done a dis-service to the public. We've seen this with tabacco, with led, and with global warming in just the last century.
And as I said: that's fine - let them publish in scientific journals, let them give lectures at universities, let them participate in scientific debates.
But as long as their opinion is out of the mainstream of their field, keep them away from discussions of that field with the general public - especially when the general public has to make policy decisions based on that field.
If their scientific arguments are not convincing to their scientific peers, then they shouldn't be given a podium to try to convince the public through rhetoric and charisma.
I wonder how long it would have taken to discover the gut-brain links if experts were not allowed to speak out of their fields. Do we also measure the credentials of the peers and check their biases before allowing them to approve arguments and enter the mainstream (whatever that's supposed to mean)?
This line of reasoning is fraught with danger, though yes we should always at least try to ensure the arguments come from expertise and experience.
The gut-brain link was not discovered by bringing in gut experts on TV to opine on questions of public mental health, nor vice versa.
I feel that you're mixing up two meanings of public debate: one is the more general notion of "any debate which is accessible to the public" (like an open-enrollment scientific conference, or publishing in a science journal), and the second one is "debating for the express benefit of the entire public", such as a news television debate.
In the first one, I completely agree with you: anyone willing to put in the work to present a rigorous scientific argument should be allowed in, even if their theory is currently way outside the mainstream, and even if they are potentially biased.
For the second one, I don't think it's in anyone's real best interest to bring in dodgy experts that everyone in their field considers to be proven wrong. Especially not 1:1, suggesting to the general public a priori that what both experts are saying carries equal weight. Particularly so in something like a climate debate, where there are 99 scientists that are convinced the evidence for man-made global warming are overwhelming for every 1 that has even a moderate doubt.
Think of the following scenario: for some bizarre reason, Congress is considering a law to forbid GPS systems to make adjustments to their clocks based on the altitude of the satellites. The public will vote on this issue, so TV stations are presenting scientific views. To be balanced, they are bringing in both a world-renowned researcher in General Relativity (say, Niel deGrasse-Tyson), and a researcher who believes Newton's law of universal attraction is the final word on the effects of gravity (not sure they could find one).
Will the public be able to judge the merits of the GR non-linear equations to understand the merits of their arguments? Or would the public be better informed by only just bringing in Neil and letting them know that he represents overwhelming scientific consensus?
But for public policy debates, I think the track record is exactly the opposite: for every major public policy issue that required scientific knowledge, inviting the reactionary types dug out by the sleazy PR industry has done a dis-service to the public. We've seen this with tabacco, with led, and with global warming in just the last century.