If you use a signed certificate that is recognised by all browsers by default it is easy for a governmental agency to subpoena the encryption key.

Cybercriminals could not subpoena that key but that would only prevent man-in-the-middle packet snooping. SSL/HTTP over TLS, or Transport Layer Security, is smoke and mirrors for normal web use.

Google encrypted its search to prevent black hat/ borderline SEO and unauthorised government snooping on their searches. The NSA probably already has Pwnage of the 'Big G'