Yes. The irrational belief that big, sophisticated organizations are scary but tiny, opaque organizations with weird names and no verifiable capabilities whatsoever are safe is a form of low-level derangement.
Are we now having a philosophical debate? It is a delusion to believe that you can "get privacy" by switching to Tutanota, and the harm of acting on such delusions is that your precious data will be delivered directly rather than indirectly to the BND. Perhaps you are thinking that it can't be a mental disorder because there are so many people who think this, therefore it is more like a religion, i.e. an obviously irrational behavior that is tolerated because of an in-group.
Mental illness is a testable set of clearly-defined symptoms that are diagnosed by a mental health professional. You are contributing to the stigma around mental illness when you toss that word around to describe something like a stupid/delusional belief. They aren't remotely the same.