Peace of mind with healthcare isn't so much about one-off costs when you catch a nasty flu. What happens if you're unable to work for months/years due to a health issue? Will you be able to pay your expensive rent and other expenses without worries?

Also you're a bit naive if you think raising kids will cost you only once they go to college. If you compare direct (daycare, preschool) and indirect (like moving to a good neighborhood) costs in the Bay area vs. a big European city, the difference is easily 5 figures year. And then there are things like parental leave.

But of course, as a 20-something you might not need these things.