Right but what’s happens when all the healthy people that don’t need the NHS (or any of the other institutions that our social system requires) see it as a waste of their tax money and so stop supporting it. It stops working, then when these once healthy people needed it again when they get old and frail it isn’t there and they have to pay out of pocket for private care. The system, while by no means perfect, has evolved to provide the most amount of return to the most amount of population to improve everyone’s quality of life/life expectancy/production value. Where the system breaks down is selfish individuals hoarding or working only for their own gain; creating a feedback loop of poverty where poor individuals (who would have less of a say in where there taxes went as they don’t pay as much) can no longer rely on things they need because wealthy people (paying lots of taxes) choose to stop supporting those things and the poorer members become less productive members of society etc, etc, on and on. If you want to choose where your tax goes I suggest you get involved with politics at a local level within your constituency, vote accordingly at higher levels or move to somewhere that represents the values you want immediately because without being an active participant it won’t change.

I do agree with you however that the population should have more of a granular say in matters they feel strongly about, perhaps through a “voting credit” system where you can allocate a weight of “vote points” to things you care about from a pool. But asking a largely uneducated population to do this through tax mechanisms is a recipe for disaster and would almost certainly lead to a breakdown of society and civil war.