So the solution is to create a secondary judicial system with no oversight so that anyone the government doesn't like can be punished for something they haven't actually done? Sign me up!
It makes sense for a minor inconvenience at the airport to require a different standard of proof from sending the person to prison.
Why wouldn't someone on the watchlist not just pay someone not on the watchlist to carry the bomb through security then? For enough money, this would be very easy to do. (It's easier if you ask, "can you smuggle these drugs in for me", though, instead of "can you help me murder 300 people".)
Everyone criminal commits their first crime. For someone, that's going to be blowing up a plane. A watchlist does not handle this case.
Look, you're reducing a very complicated issue with a huge amount of nuances and details to an easily refutable straw man argument. Life in a modern society requires recognition of different types of law violations, different types of punishments, and different acceptable response times. In order to operate in fair and effective manner, all of these require a different standard of proof. Putting a person in prison requires proof beyond a reasonable doubt. Having a person compensate someone financially requires 50% + 1 of the jury. A parking ticket requires a quick decision from a bench judge. You could set up a system where a parking ticket could be contested by a trial by jury, but this cannot be practically implemented without a huge strain on the legal system.
TSA agents have to make a simple decision - whether to do a detailed search or not. This cannot be done to every passenger, the decision must be made fast, and it can affect other people's lives. It is not in any way a "punishment", only a minor inconvenience. In this case suspicious activity is a reasonable standard of proof for a detailed search. If you want off the watchlist, you should be able to have a hearing to clear your name, you should be notified that you've been added to such a list (barring some exceptions that should require judicial oversight), etc. Nobody is talking about a secondary judicial system with no oversight. You're picking the worst possible implementation and shooting it down - this really isn't productive.
Why wouldn't someone on the watchlist not just pay someone not on the watchlist to carry the bomb through security then?
For any possible security measure you could come up with a countermeasure that would theoretically render it ineffective, but that doesn't mean that we should sit back and do nothing. It does mean that we should attempt to find a systematic, scientific way of measuring cost vs. benefit of any proposed measure, but this is a difficult, time consuming problem. Until we do, we should implement security measures that appear reasonable. To give a counterargument to your specific complaint, a watchlist significantly complicates the job of a potential terrorist. The more people know about the job, the higher the probability of a leak. I will conjecture that the probability of a leak with respect to the number of people that know about the job isn't a linear function, it's likely closer to exponential, which means forcing a potential terrorist to recruit someone not on the watchlist might be a cheap and effective way to ensure that a leak happens. I don't know how effective it is in practice (I'd be interested in seeing large scale studies), but until we find out, intuitively it seems like a good idea.
Do you similarly think sex offender lists are a joke?
Until we have murder offender lists, traffic violation list, and credit-card-bill-underpayment lists, yes. Why only shame sex offenders when we can exile everyone for one mistake?
I think the next step is to require sex offenders to wear little stars on their clothing when they go outside. That way they can be recognized and treated appropriately. I hear that worked pretty well for getting rid of Germany's Undesirables.
And, we know the no-fly lists are also a joke.
Unless the Penis Bomber also burned off all the memories of the "2-year-old Toddler Not Allowed To Fly" and "Senator Not Allowed To Fly" etc new stories from the past 6-7 years.
It's sheer populism, pandering to the worst impulses of everyone. Bad bad bad -- not to mention ineffective.
The 9/11 hijackers had valid passports, visas, and were not on any watchlists.