a) Governments have already effectively made it impossible for people to use bitcoin as a medium of exchange, as they expect taxes to be paid on bitcoin gains.
I dont know where you are from, but where Im from you pay taxes if you gain money commercially no matter if its BTC, USD, AUD or EUR. If I buy something private I dont pay taxes, wether I pay with BTC, USD, a local currency or chicken. So this point is invalid.