This is a pretty disingenuous and misinformed response to someone stating that the marijuana issue is not very pressing:

"Non-violent crime" is not limited to marijuana, or even drugs in general. It includes theft, embezzlement, arson, fraud, every kind of white collar crime, drunk driving, gambling, bribery, pretty much anything that doesn't involve harming or trying to harm someone. To say that "millions of people go to prison for non-violent crimes" is only vaguely and very broadly relevant to the assertion, you need to go more specific. And when you go more specific you find that, based on recent estimates the number of people currently incarcerated for possessing or selling marijuana is 20,000-30,000 or 1% of the total inmate population in the United States. Source, near the middle, control+F: "While the number of people behind bars" to skip straight to the relevant paragraph

We can argue the number should be zero, and I agree with that. But you're doing a disservice to the cause in question by resorting to such inaccurate and misleading hyperbole.