For the case of terrorism, terrorist can easily purchase weaponry from other country. With the use of transaction using bitcoin, authorities will have a hard time tracing that transaction thus, will give advantage to the side of terrorists.
This is not an impossible scenario. People can now use bitcoin in any way they want to. It's inevitable.
If bitcoin was to have any significant utility - which it hasn't - it would be to allow the financial aspects of what you call terrorism and crime. After all, that's what economic freedom is about: being able to spend/finance whatever you want with what is yours. If you want to finance terrorism, this is your good right, and a good permissionless currency should allow you to do so. If it doesn't, it means that it is not the free, permissionless currency you thought it was.
In fact, the ultimate test of whether a payment system is truly decentralized and permissionless, is: can I finance terrorism and crime with it ? If I can't, it means the system isn't truly decentralized and permissionless. It is the ultimate test of a freedom currency.