[pictureofabear]

Right, but you can test this real-world with much lower stakes. Airliner aircraft are relatively cheap and easy to acquire.

SCUBA gear is for diving underwater where pressure increases, not for breathing high in the atmosphere where air pressure is lower. There are plenty of suitable breathing apparatuses made for breathing at altitude. SCUBA gear and knowledge is irrelevant to this situation.

There are a multitude of ways to target an individual or a particular piece of cargo without killing so many people in such public fashion.

The attempt to use abductive reasoning here falls short because you're choosing the least likely explanations when far simpler and more plausible explanations exist.

Conspiracy theories like this often, at their heart, rely on an assumption that governments are either irrational or have hidden motivations, but both of these assumptions require a heavy amount of evidence to outweigh all of the evidence to the contrary.