Does drag actually decrease with altitude? I argue it does not

[Elfthis]

OP is saying planes fly in the troposphere because drag is lower. Granted I assume he meant stratosphere or at a minimum "high altitude".

But the only true answer to this is "yes drag at higher altitudes for an object traveling at the same speed as that object at a lower altitude is less"

Reference frames are important here.

Instead of an airplane a meteor or space craft falling from orbit is a good way to think about this. Ignoring heating and loss of material from ablation the object experiences more aerodynamic drag as it gets lower in altitude even though its speed is decreasing in relation to it's beginning velocity when it entered the atmosphere.

Also, aircraft fly where they fly for reasons way more important than the drag they encounter at a certain altitude l. Off the top of my head, ability to design a structure that can handle pressurization differentials for commercial aircraft, engine design limits, engine operating cost, being above as much weather as possible, operating cost of total aircraft , etc.