Obviously the one that is more of a widespread issue. Obesity costs more money to deal with because there are infinitely more obese people in the world than there are who are addicted to heroin. Fast food is legalized which means criminal organizations aren't going to cash in with it, but it does mean more people are going to be eating it because it's easier to obtain.

Certain narcotics are very clearly adverse because they are extremely addictive with very very small amount of use. You argue against "clearly adverse narcotics", does that mean you think it is responsible to make all narcotics legal? Should people be able to get heroin as easily as they get cigarettes, never mind the kids who would easily be able to go get some dude to buy them a hit of heroin or meth.

One mistake run with heroin or meth can fuck your life up for good, no matter what kind of person you are. Proper education and good life styles are a much more effective defense against drugs then legalization.