"Once the owning class owns mostly everything and has intelligent machines that serve them, The Economy crashing will not have real consequences for them."

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This assumption is not necessarily valid. If things get bad enough for the masses, things will become even worse for billionaires. Inequality fuels revolution. Bunkers and security bots will not save them.

To put it another way, if you have command of the resources to do whatever you want, does it make sense to use them in such a way that your future is to cower in an underground bunker?