Here's another way to look at it:
Suppose pot was already legal and had been for generations. What arguments could you make to convince people it should be made illegal and that we should be throwing people in jail for having or using small quantities of pot?
If you are having trouble imagining that, try imagining it with something that's now legal. Suppose we decided it would be a good idea to ban coffee and to throw anyone caught owning, selling or drinking coffee in jail. Sell me that argument.
Look at the amount of trouble we (as a society) are having convincing people to scale back on sugar. Imagine if we tried to make sugar illegal, including all sugar-added products. There are probably much better arguments for that than for banning pot, yet that would be a tough sell.
Coffee is addictive and a gateway drug. In fact, it was my gateway drug http://www.newportacademy.com/coffee-the-new-gateway-drug-for-teens/