That same argument applies to alcohol, tobacco, or a poor diet, which likely incur even higher externalized costs. Do you believe we should criminalize those, too?
From "Libertarian" premises, however, the solution to those costs is that smokers, drinkers, and people who eat poorly should pay higher healthcare premiums to offset the increased costs they incur.
The problem with that, of course (and a big part of why I'm pro-single-payer) is that people who eat poorly, for example, are disproportionately poor, themselves. It turns out, it's expensive, in terms of time and/or money, to eat healthily, and the poor, especially the working poor, tend not to have one or both of those to spare.