Usury is a action where loan is given to person based on the condition that he should pay a certain percent of amount as interest irrespective of whether he gains profit or not.If usury is banned and interest free loans are given, it will be good but today we dont find any such options.In some islamic countries,islamic banking system is followed as an alternative option. I dont know how banning usury will promote crypto currencies because usury is a financial option and crypto currency is a trading option.They are not inter related to each other.