Boeing, as well as many other firms, are just too big to fail suddenly.
Are we sure it's a pillar? Perhaps if you take all of the suppliers and partners it represents, sure. But by itself, I don't think it really look all that impressive.
After The War, the US government was careful to keep domestic manufacturing 'healthy' which turned into 'fat and happy' which has now turned into I-don't-know-what, but I wonder if subsidies-as-defense-policy should be putting more energy into other industries.
Also, who cares about the Dow plunging if it's for such a clear and explicable reason - it's usually used by politicians to gauge mysterious impacts on the economy, when you know the cog that broke to cause the numbers to swivel it's a pretty useless metric - you already know the thing.
It's sort of like not wanting to go into maintenance mode to deploy a big infrastructure patch because being forced into maintenance mode is bad - yea, it is, and if you can avoid taking servers offline go ahead and do that - but if you can't then just eat the outage as it's probably better to upgrade things than to refuse to upgrade due to the fact that it will expose the fact that you had to upgrade.
The enormous fraction of people who have their retirement savings tied up in the stock market, that's who.
We'll be fine.
Also known as "a systemic risk".
This is the downside of allowing the concentration of economic power in too few hands. It's like other large scale systems. Yes there's a lot of redundancy; but that redundancy serves a purpose.