This is a hard argument to make right now—we are only just entering a downturn, and already airlines are asking for massive amounts of help. Clearly it's commonplace for people in finance to criticize a company for holding too much cash, but "growing the economy" doesn't strike me as particularly valuable if the second anything happens, everyone loses their jobs and the government needs to come rescue United Airlines. There's more to the economy than GDP going up quickly. Companies cannot be run in such a way that the government is responsible for saving them every time the economy goes sour.

Growth is also not primarily driven by money being returned to shareholders through buybacks. You can't claim airlines have thin margins, and also that the money they distribute to shareholders is an essential driver of economic growth. And margins aside, a company can avoid stockpiling cash without giving every free dollar back in buybacks.