Schneier has less expertise in airport security than other professional security and law enforcement people who also disagree strongly with the TSA's approach to airport security.
My point isn't that "it's bad security" is a losing argument; my point is that Schneier isn't the only qualified person making that argument.
If a half-dozen more qualified individuals step up to make the same arguments, perhaps the inclusion of Schneier would prove redundant. I don't see those people lining up to make those arguments, and I see plenty lining up to defend the current state or try to make it worse.
It also helps to hear from someone who starts from the perspective of "only do things that work and are worth the cost", rather than someone who starts from the perspective of "do anything that could possibly make a difference, it couldn't hurt (given that we don't place any value on anything other than security)".
When you get down to it, there are broad and poignant parallels between airport and computer security, and similar problems with each. Both fields have tried and true, yet difficult-to-implement best practices (well-trained screeners a la Israel, and operational security such as "don't open that shady email"). Both industries suffer from a proliferation of charlatans, and both industries have customers who are more concerned with the appearance of doing something useful, than going through the pain of implementing actually useful best practices.
Schneier's as well-qualified as any to speak to the stupidity that pervades both industries.
That may be true, but Schneier is also a good figure head for a vocal minority. Schneier may be able to throw around his weight better, or may be more skilled at debating the broader issues.
My point isn't that "it's bad security" is a losing argument; my point is that Schneier isn't the only qualified person making that argument.