Obama was asked about legalization of marijuana, and I guess he thinks the suggestion is kind of funny and doesn't merit much by way of response. For Obama extremely popular positions are laughable.
Why is this laughable? For good reason. It has nothing to do with protecting Americans from damaging health effects. Setting aside marijuana, which kills about nobody, all hard drugs combined kill relatively few people. If we really cared about the health of Americans we'd decriminalize drugs, since that would be expected to improve things.
There are two other major factors at play. First we have a for profit prison industrial complex, which is pumping millions of dollars into Washington as part of lobbying efforts to keep incarceration rates high. That's profitable. The additional issue is that the CIA needs money to run covert wars. Better to sell drugs than ask Congress for money, since that is more likely to bring the wars to light. Ron Paul discusses these issues back in (I believe) 1988.
For a discussion of the centrality of CIA drug trafficking in the Nicaraguan Contra terrorist war directed by the US, watch Iran Contra Coverup.