It will lead us to a place where some Americans, having been given the freedom to "do" drugs, will try it out and eventually decide it's a stupid thing to do. Others, given the same freedom, will feel no need, desire or temptation to "do" drugs at all and will not change their attitude at all. Others will become addicted and will need help getting off of the drugs; some of them will recognize that they have a problem and will seek help on their own; others will have friends and/or relatives that will recognize the problem and they will be encouraged to find help, which some will deny; others may die as a result of "doing" drugs.
Those who try it will probably learn something (good and/or bad) from the experience that they can pass on to others. Hopefully, in the end, it will lead to a society where the "forbidden fruit" factor will no longer exist, thereby resulting in fewer people feeling the need or the desire to use drugs "recreationally".
But I think it's a pretty safe bet that it won't lead to an entire society of drugged-out zombies that causes America to crumble and disappear overnight. If it does, and thereby goes to show that there was nothing between America and utter ruin but the willingness of some Americans to punish other Americans over drug use, then it's probably reasonable to assume that America wouldn't have lasted much longer anyways, and was ready for the garbage heap of history.