What legitimate liquidity aggregator is going to hold the counterparty risk for PotCoin/HempCoin and have banking relationships? Because once the Weed-coins are sold for BTC and given to a liquidity aggregator in jurisdictions where marijuana/hemp are illegal that becomes money laundering.

Cryptocurrencies that dodge regulations do not; their value is backed by the greater fool theory and the fact that this new retail wave aren't too familiar with AML/KYC/counterparty risk

To address your last point, a non-gubmint backed stablecoin would address that, but then again, perpetual motion devices would probably stop energy issues.