Constitution doesn't forbid it, and it reasonably falls under prudent governance per both precedent and the constitution... the constitution doesn't authorize you to fly airplanes either.

I'd give the airlines a pass on moral hazard on this one, because they were mostly positioned to weather a 9/11 type event or other typical downturn. Loss of essentially all revenue for 4-8 months was not what anyone would have considered a plausible scenario two months ago. There's no precedent for this.

And the airlines are a very key economic pillar... the economy will not come back without them, or at least not as anything recognizable and certainly not within a decade. Too many other sectors would have to completely collapse and then re-invent themselves, or be replaced by something new. That would take 10-30+ years and result in global human misery beyond reckoning. And war, don't forget that part... plague and famine don't tend to ride very far without their two brothers.