If a criminal uses BTC as payment method he is clearly stupid and does not know the privacy limitations of Bitcoin. There will always be criminals, and they will always find creative ways to pay for their operations.

The crypto space have developed a few privacy coins which will assist the criminals but it is important to realise that privacy is not equal to illegal. Even if you have nothing to hide I'm sure that you do not want everybody to have access to your account.

Image that your neighbor can access your BTC account if they have your public key.

Privacy is a right, what you do with it is dependent on the motives of the individual. Obviously the best, and most private currency is cash.

Just my thoughts