Well... one point that must be made is no president is allowed to act upon (or even show) his personal interests, views or beliefs. He is there just representating the interests of the actual owners of the country (great corporations owners, great bankers, etc), and thus he must act accordingly with this.

Even if Obama smoked weed and liked it and wished in his heart to legalize cannabis, he still would have to follow the script written for him and act like if he were against it, and even laugh about it. Being president is just playing a role, and he just played it as he should. Who can know what was he actually thinking when he laughed?