I am reading many people's view that they only flag this when intentional. Is there ever an occassion where this should be flagged even though not fully intentional?

I believe that it is incumbent on the defensive player to keep his head up and ensure that he doesn't intentionally or unintentionally make initial contact with his helmet in a way that may create a safety issue.

So, I guess if the defender (or offensive player) initiates the contact with his helmet in a punitive manner (vs. a football related move), then I would flag him.