If I may, what you're advocating is known in the security biz as "security through obscurity." It is notoriously ineffective, as anyone with any degree of initiative can easily "defeat" this security mechanism. (You can validate this yourself by Googling the phrase "security through obscurity"--the articles which come up will almost without exception be disdainful of the concept.)
In this case, this information needs to be widely disseminated, as the aviation community (both professional and private pilots) need to be on the same page as the air traffic controllers at all times. Any attempt to keep this information secret is doomed to failure, as too many people need to know this "secret." Therefore, we must assume that the bad people know this information, and act accordingly. Posting the squawk code information once, twice, or a thousand times on Free Republic or elsewhere on the Web has no meaningful effect on aviation security.
If I recall correctly, you've got a personal stake in this (was it your husband that was a pilot?) so your position is understandable. But I think if you asked 100 security experts, 100 of them would tell you that it's not significantly more risk to have this information out in the public, and may in fact be safer than trying to keep this information closely held -- (i.e. a scenario where a private pilot either did not know or forgot the codes, putting his/herself, the fighter pilots, and possibly the public at risk thereby.) Security is the business of risk management, not risk avoidance. Pros and cons of any action taken for security purposes need to be carefully considered.
Having said that, I'd agree that it would be prudent to investigate some kind of rotating encrypted code system rather than the static code currently in use--maybe adopting the SecurID passcode technology for instance. However to implement that, you'd have to replace (or augment) the transponder systems in every single airplane in service. Smarter people than me are probably looking at how to do this right now, but it is a massively non-trivial problem to solve, not in the technology but in the deployment.
Sorry about going on at some length, but I thought your concerns needed a more thorough discussion. I'm sure other security-savvy FReeper can chime in with more detail.
I'm sorry. Policies and procedures do not need to be shared online. For example, do we need to know how many air marshalls are being implemented on passenger aircraft? Do we need to know where they will sit, and what they will have on their person as weapons?
Heck, then why not share one's medical records and SS#? How about just posting one's credit card information right here? Let's widely disseminate it. Why even classify documents in the military? Let's all share and be friends.
For me, it all started when CNN met our "covert" operations on the beach during the Gulf War. It begins with each of us being responsible and zipping our mouths. Should our POWs flap their gums to their captors b/c anyone might be capable of finding things or hacking into them on the Internet? Should graduates of SEER school share their experiences with those who have yet to attend? How will that prepare them in real life? Should this be shared on the internet, too?
Where would you (and others) draw the line?