Well, by removing the privacy cloak on cryptocurrencies; making it mandatory for all exchanges to verify your data the same way banks do.
If they could match address with person, then it's no longer like cash. If they forced every exchange (and BTC accepting businesses) to comply with KYC policies and criminalise any p2p BTC/fiat exchanges, then any 2 people could still send btc to each other, but the moment you try to cash out or buy something officially, you'd have to be prepare to explain where did you get that bitcoins from.
They could try get you when cashing out but hopefully you won't need to ever cash out, i can pay all my bills via bitcoin and the more accepted it becomes the less likely people will have to "cash out"