The constitution provides no real limit on the powers of the state. It's a government court that decides if there are any violations. And most violations never make it to any court. Only our societies diminishing respect for individual rights keeps the government from doing whatever it pleases.
What private police force would outlaw marijuana? There would have to be a large number of clients willing to voluntarily pay to fund an intrusive drug war and that is highly unlikely. The market would not support such action and neither would it support a service that gang rapes individuals for such a "crime."
Your views are more insane that the status quo.