You can always stay and be a lapdog for their experiment. Choice is yours. But perhaps you didn't understand the nuance here. Everybody is understaffed. Everywhere. If a large group of people threaten to quit all at once, who will do their work? Basically what I am suggesting is to call their bluff. They threaten you, you threaten them. You'll win because they can't afford to let a ton of people go.

Also, your last statement is not true. Smart people think ahead and plan, so yeah, maybe a lot of people aren't, but there are plenty who are and can.