The trade off that made the ACA possible was clear to everyone at the beginning: The mandate will bring the insurance companies more customers and that will help pay for the sicker customers they will have to cover. If it doesn't work out the federal government will be backstopping their losses.

Optimism around insurance stocks reflected in their stock prices was all about larger volumes making up for smaller margins and lower risk, there is no tricky misdirection going on here. That is "all you need to know about this story".