hi tkc,
it's a fun thought process to consider. to an extent, i think you are experimenting with the idea to see what comes back, maybe.
here's why i think we don't discriminate.
because we share medical costs across the whole of society, rather than differentially. that's how a medical insurance system works. those that don't need help partly bear the burden for those who do.
otherwise you say, well, that person has cerebral palsy - let's exclude them. because money.
or using your model, i might argue that old people cost more than young people. so they should pay more. but for insurance purposes, we need young people to participate to spread the cost. and across a whole life, we all end up getting older.
similarly, we are all the product of male sperm and female eggs. we all require a person of the opposite sex to produce a child. so in order for the species to survive, we are all in this together.
it isn't about individuals. it's about sharing access to healthcare and sharing costs in a way that understands you might be the next patient and you may want the help yourself.
i might also apply the equitable principle that no one ought to be discriminated against for inherited characteristics. a person born female did not choose to do so. hence, they shouldn't accrue disadvantages as a consequence. same as we treat people of different skin colours equally. but under your principle, we might say that black people should pay extra because some of them are more susceptible to sickle cell anemia.
that's a couple of reasons that come to mind immediately. i think there are many more.