The more I think about "Frank Castle, Secret Agony Aunt", the more I like it. Of course he'd have to use an alias, which presumably Karen would choose. What would she pick for his Agony Aunt name?

Just don't, OK? You're not protecting anyone, you're just allowing them to go around "blind" (pardon my pun) and be in danger *because* of their ignorance.

Every superhero should have this tattoed on their forehead. Or something. Laudable examples of superheroes who do tell their friends can sponsor them in "Secretkeepers Anonymous" classes.