We as a society accept the insurance system as an implementation of "funding healthcare" because market capitalism is supposed to lead to lower prices, fair allocation of scarce resources, and innovation, among other things. That is, the insurance industry is a market solution to a moral problem.

If insurance companies then can wiggle out of covering pre-existing conditions, they're no longer solving the moral problem they were brought into the world to solve, and now we need some other solution to solve the rest of it. Then, whatever that other solution is, it's solving the hard part, so why not extend it to solve the whole thing and cut the insurance middlemen out of the economy entirely? What are they even doing at that point besides extracting a rent?

(This is one answer among many good ones to what is really a bad-faith question—health-insurance is not a lot like fire-insurance at all)