If by any means criminals start adopting crypto in mass (especially privacy coins), we could expect a full government crackdown on the entire industry. Which is why I think it's best for criminals to continue using Fiat for the sake of the crypto/Blockchain industry's growth worldwide. But we'll never know what will happen in the future. Thoughts? 
Like what you have mentioned, a learning curve in in cryptocurrency is required when you start using the said currency. Compared to fiat which has been the conventional payment that existed since time immemorial, the convenience and accessibility is already preset unlike in cryptocurrency. Although transactions are completely anonymous in the latter, one must still have to learn the fundamentals before they start transacting.
I think people with a criminal mind ready to act on and undertake illegal activities don't care whether it is fiat or crypto as long as they can obtain them with minimal effort and get away with it.
I also agree with this statement. When a criminal has already decided to commit a crime, regardless of the nature of payment it uses, as long as it achieves its goal then it would exercise all the means just to make it happen.