John Adams, the 2nd President of the United States said "Our Constitution was made only for a moral and religious people. It is wholly inadequate to the government of any other."
No he wasn’t but he didn’t advocate making drugs illegal either. You could to to the general store and get laudnum and knock yourself out is you so chose. He also didn’t put a prohibition on alcohol. Nanny statism and religious statism don’t coordinate well with the constitution.
Pot doesn’t make people rob steal or rape it just makes people goofy and hungry.
That's a valid argument if your objective is to argue that the existence of porn or pot means that the Constitution should no longer be in effect. If that's the case, then there's no constitutional argument against Obama's legitimacy as President, or any of his programs.