Not all criminal activities can be linked with Bitcoin
Bitcoin cannot be used with any kind of criminal activities
But we can can agree that with the use of Bitcoins, those who are into ransom has increased their chances of not blowing up their cover.
Those who use money as payment to drugs, gun smuggling can use Bitcoin to pay and remain unknown
However, not every criminal in this world are into this kind of technology, keep in mind that there are more small time criminals out there that those who are big time and small time ones prefer cash and fast money.
I agree with you, not all criminals use btc in their bad activities, because not all criminals have an ideas how to use it, but maybe this is the simple way to make their transactions faster and they can hide their personality. Maybe those big time criminals used btc on their illegal, because they want to get easily money. But before it was created their already criminals in this world, i think they will not use bitcoin in some illegal activities.