You incarcerate people who break the law of the land.
Just like all around the Western/Judeo/Christian civilized world.
Even where we align with the Muslim world over some laws such as homosexual marriage, the degree of enforcement may cause us to part company. For example, one may feel that homosexual marriage is wrong but we in America are disinclined to stone people to death for engaging in nuptials with people of matching genitalia.
It is no answer to say that we enforce the laws because they are the law which is essentially what you're saying. That is only a tautology. We must, inter alia, be able to defend the wisdom of the law, the manner of its enforcement, the efficacy of the law, it's social consequences, it's effect on individual liberty.
I suggest that the war on drugs has failed every test. The more we enforce it, the more we fail.