Not at all. The name of the game is keeping the transmission rate low. Catching some infected passengers (even if not all) serves that purpose directly and effectively. Nothing remotely "theater" about it.
If by "effective" we mean "reduces the transmission rate of the virus" then yes, temperature checks, wearing masks, washing hands, testing for the virus, physical distancing... these are all effective ways to reduce the spread of the virus.
By that logic, you can justify literally anything: if it might have some theoretical impact on “transmission rate”, you do it because doing something makes people feel like they’re doing something.
We know that infected people can spread COVID19 without any deliberate action on their part through the simple, reflexive action of exhaling. This part is not in doubt. The virus has an R0 greater than 2 in uncontrolled circumstances, meaning that each infected person will likely infect at least 2 others. This is the lower bound; other analyses have placed the uncontrolled R0 for COVID19 as high as 6.
Thus, identifying and quarantining as many of those who are infected as possible will reduce the transmission rate because there will be fewer opportunities for those infected people to (unwittingly) infect others. This part is not in doubt. It's basic physics and basic medicine.
You’re focusing on the “virus scary and contagious” part, and skipping the part where you show that the proposed method is effective at stopping it.
As many others have noted now, if I can bring a test result taken days ago, I can easily have acquired the virus in the meantime. On the plane, for example. As you note, respiratory viruses are usually contagious, and there’s an incubation period where you probably won’t test positive or show symptoms.
I will stress again, the name of the game is keeping the transmission rate LOW, not bringing it down to zero. Do you think 6 feet prevents all droplet transmission? No, of course not, but it helps reduce the transmission rate. Do masks prevent all infection? Absolutely not, but it helps to reduce the transmission ate.
If we can devise low impact ways to reduce the transmission rate (masks, chokepoint testing, remote temperate checks) then we can do away with the more onerous methods (closing down the entire global economy for example).
You may recall that we shut down the entire global economy because of this virus. So yeah, it's true, we can justify a whole hell of a lot in service of keeping the transmission rate low.
And there's nothing theoretical about this. Regularly stopping infected individuals form boarding planes will reduce the transmission rate, not in theory, but in fact.
Because the name of the game is keeping the terrorism rate low. Catching some potentially-dangerous passengers (even if not all) serves that purpose directly and effectively. Nothing remotely "theater" about it.
My personal opinion -- and opinions may differ -- is that yes, the TSA is security theater.
To my knowledge, the TSA has never caught a terrorist.
Moreover, the Department of Homeland Security conducted a test where they attempted to smuggle weapons or mock explosives onto airplanes. 67 out of 70 times, they succeeded.
The point of the TSA is to be the first hurdle in a multi-tiered approach to preventing terrorist acts on airplanes. It was never meant to be the only mechanism, nor even the primary mechanism.
It was simply intended to raise the difficulty of getting weapons onto a plane enough that terrorists would choose other, easier options. It's irrelevant that DHS can get weapons onto a plane--there's no risk to their agents when they get caught since they can just flash a badge and move on with their lives. If a terrorist gets caught with actual weapons, the consequence is failure and imprisonment for the rest of their life. The risk may be small, but it's significant enough, and it's just the first hurdle. (There are additional hurdles, like locked cockpits, randomly-assigned US marshals on most high-value flights, and 100s of fellow passengers that a would-be terrorist must also contend with.)
And it worked. Terrorists in the West shifted their goals away from attempting to bomb/hijack planes and trains to simply renting trucks and trying to drive them into crowds. This is why bollards began surrounding so many areas that draw large crowds, like sports arenas and pedestrian thoroughfares. (In the U.S. bollards have been required for federal buildings and mass-crowd facilities like Sports Arenas since the Oklahoma City bombing. After a mass-fatality driving accident at Santa Monica's Third Street Promenade, California began requiring them at outdoor malls as well and this has become standard practice in the U.S.)
