Give it up. It's a cultural issue, not a government issue. Since pot smokers are perceived to be liberals, they are fair game for the right. Rush can suck down cigars, pop pills, and get divorced 4 times and he's a pillar of the community, but smoke a bone with some friends and you deserve jail time. That's your culture war for you.
That's basically about it; deep down people don't want to give the people who they perceive smoke pot the satisfaction of legalization (long-haired hippies) rather than any really rational reason for not ending this part of the WOD.
Unfortunately, when 700,000+ Americans are arrested annually for pot while illegal aliens continue to pour across the border and terror cells plot their next move, it most certainly is a government issue.
A government with a very poor sense of priorities, that is.