A user with the intent to engage in unlawful activities should read the terms of services in full. If that user only reads the homepage of the service, without understanding the implication of each word, and does not bother to review the terms in details, that is on him.

Moreover, I would like to point out that ProtonMail is about encryption of email *content*. It is foolish to expect more from them. They won't protect your identity: law enforcement can know who you are and who you communicate with, but they cannot know the content of your emails (if you recipient uses encryption services as well).