Hrm, I can definitely see your logic there. However, I have actually been thinking about this, and I am hesitant to add locking chests for several reasons.
First, I feel like adding lockable chests puts a layer of distrust on the server. Like, we need lockable chests because we dont trust everyone else. Right now, the 'guest' group cannot open chests or take items, so I am not too worried about them. And I honestly feel like trusting everyone to not be jerks and steal is better than assuming that someone will steal.
Second, right now, I am allowing anyone who wants to play on creative to do so. So really, what would be the point in stealing when you can just go into creative and get however much crap you want.
It really seems like our server is in a awkward state of being. On the one hand, I want to play legit because it is more fun and adds more meaning to my game-play. On the other hand, I don't want people to be held down and have to play legit just because I want to. Obviously these things dont really mix well when it comes to trade and interaction.
So basically I am rambling and I dont know what to do about any of it. :D
But if more players want a locking chest system I will add it in for everyone, np.