Lt. Gov. Josh Green hopes to reopen Hawaii’s tourism industry by July

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.)

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.

That is not itself a justification for doing more of them.