While your conclusion is true, for-profit prison systems are a clear conflict of interest and certainly influence media and lobbying. Law enforcement has spread its fair share of misinformation and unnecessary violence, as well.
There's a lot of blame to go around. The prisons share a whole lot of it.
The bottom line is that the thesis underlying most of the comments in this thread is wrong. For profit prisons, police unions, etc, are not the biggest roadblocks to legalization. They're opportunists, but the backbone of the drug war is massive support from soccer moms and dads, the reliable voters that created the drug war in the first place. And if the medical community starts chipping away at them, change will follow, regardless of what the prison lobbey wants.