Fair enough, some risk exists, and how much probably depends on the position ... although in my country as far as I'm aware, there is no requirement to give notice (it's just a courtesy) and, of course, no such requirement exists on the part of employers.
In the linked article, it's mentioned that Elon felt a constant need to fire people that he sometimes had to be talked down from, so if the employer risk exists, it doesn't seem to be particularly high in most cases. If the risk for employers was significant, then at-will employment laws wouldn't even exist, because the entire purpose of such laws is to make it arbitrarily easy to fire employees.
The only way at-will employment could truly be symmetrical is if I could walk into work and literally fire any of my managers or the CEO with the same ease with which they could fire me.
But of course, actually applying the power dynamic of at-will employment both ways would just be insane wouldn't it?