Yeah the fact that you cannot be traced via Bitcoin is making it the ideal place for online criminals. You will never be able to stop all criminals so just do not focus on them.
yeah it would greatly assist criminals in their illegal activities will not be easy in recognizable by making a payment or transaction with bitcoin. thats why government prohibit it
bitcoin is not that anonymous,bitcoin still can be traced,and can be explored because it's published widely without privacy or even if you'd write a notes on your transaction it can be readed by another people on internet