This is how insurance works. We pool everyone. You're not buying specific health procedures. You're buying decreased risk.
No, that's not how insurance works. That's how charity works (or wealth transfer, a.k.a. theft, when it's forced). True, you're not paying for specific procedures. However, you should be paying according to the probability and cost of the procedures you're covered for. A procedure you'll never need has zero probability, and thus shouldn't affect your premiums.
You're not buying decreased risk. Risk is the product of probability and cost; if anything, insurance increases your risk by adding the insurance company's overhead and profit margin. It certainly can't decrease risk for everyone no matter how you structure it; there must always be at least as much payed in as the insurance company pays out, on average, or the company goes bankrupt. The purpose of insurance is to reduce the cost of an insured event to something manageable, in the event it does occur, at the expense of increasing the probability of paying that cost (you have to pay the premiums whether the event happens or not).
The idea behind insurance pools is to group together statistically independent policies of about the same level of risk. They don't necessarily have to cover the same things, you just want to avoid holding a bunch of cash in reserve, or else bankrupting the company in the event several large claims have to be paid out at the same time.