Stealing wouldn't be a deal breaker for me...I guess I should preface that with the need to see how it was done first. My gaming history includes UO, so I'm accustomed to a system that allows other players to try to "look in your pack and steal something". Heck, I was there when "that player who shall not be named" stole the firewall scroll from another player in UO and set Lord British aflame.
That said, based on the point that we are not sure that we'll have direct player to player trading at launch I doubt there will be direct player to player stealing. They are essentially the same action afterall. Course, primetide could prove me silly!