A better question to ask is why they felt the need to have to hide something in a diary and not communicate with you? I post my diary on the web for all the world to see, I have nothing to hide from anyone and actually have a little pity in my heart for those people who think that they can't be themselves and let the world love them for who they are!
Different people have different levels of comfort.
I'd say yes, it would be justified - when they say you can.
