[ndsipa_pomu]

The idea behind taxation is to enable collective spending power for things that ideally benefit society. The NHS is likely to be useful for the vast majority of people at some point or another though individuals may well not get value for money if they're healthy or die young etc. However, providing free/cheap healthcare enables people to get check-ups and hopefully catch problems earlier which can make a huge difference to the outcomes. Of course, increasing the health of the workforce is going to benefit the economy as well, if you're looking for a purely monetary benefit.