If you want to subsidise these unfortunate people, please just do so openly. Don't be all sneaky, sneaky about it by banning accurate risk assessments.

In any case, what you are saying is only true, if you buy your health insurance second to second on the spot market.

Insurance companies are more than happy to enter long running contracts, where you both agree today on (the algorithm for) the premiums for the next twenty years or even until the rest of your life. That's pretty common with life insurance and disability insurance already.

The above already exists, but if you allow some speculation: you could even envision people buying insurance for their kids before conceiving them. That way you don't have to worry about pre-existing conditions.

(Well, if the parents already have heritable conditions that would make the kids more likely to have expensive medical problems, those would push up their premiums. But then: perhaps these people should think twice about burdening a potential kid with these issues.

Compare how in Cyprus where sickle cell anemia is prevalent, even the Catholic church demand you get screened, before they'll marry you.)

If you really want specialised in-kind welfare, you can get people a voucher for the catastrophic version of 'unconceived baby insurance'.

Basically, you can buy insurance against insurance premiums being expensive.