I thunk that alot of new inxperienced FO's do not realise just how inexperienced that they are.
I would never want to discourage an FO from challenging my actions if they do not think that they are correct but to have your every actioned questioned is very wearysome, especially when it is an issue of different ways to skin a cat. (Sorry veggies).
Perhpas though that the more "assertive" of new FO's might want to consider how they word the challenge (I am not talking about a blatant safety issue). Perhaps soething along the line of, "For my own learning please can you tell me why you did xzy that way?" would be more appropriate than, "Capt, I think that there is a better way of doing xzy".