Not being in the Constitution does not mean it's unconstitutional. There are a lot of things we take for granted in today's United States that weren't in the Constitution either.
Being the only real industrialized nation without healthcare, especially one with the largest GDP, says a staggering amount. We could easily pay for a lot of the stuff we should have and move towards a surplus budge, but the moment Americans here the word "tax" their asshole shrivels up. We're one of the what, three or four least taxed first-world countries?