''Congress can certainly regulate interstate commerce to the extent of forbidding and punishing the use of such commerce as an agency to promote immorality, dishonesty, or the spread of any evil or harm to the people of other States from the State of origin.''
-- Chief Justice Taft, Brooks v. US, 267 U.S. 432 (1925)
There is no basis in the Bible or even in the history of jurisprudence to suggest the use of recreational drugs is immoral, or evil. Like anything they could be harmful, but so are most prescirption drugs if used wrong.