My ability or inability to talk someone out of robbing me is irrelevant to whether my concept of morality is rational. A person who steals is making the baseless claim by his actions that he is inherently more valuable than others. If I present you with two E. coli, can you say which is better and more deserving of life? Which house mouse has more inherent value? In the same way, there is no rational basis for claiming one person is "better" than another--it's a meaningless claim. So the thief would be acting irrationally.
Wrong. The premise of God allows a rational argument to be made for morality. The athiest has no premise that meets the same need. Further, the individual you talk to about God can be touched by God himself; the key premise is provable in his own experience, God willing. It is a relationship with God, not a set of rules, or a moral code, that is the key to life. Nonetheless, the premise of God allows the argument for morality to be made where no premise outside of God serves the purpose and is consonant with each individuals experience and reason. Doing harm to others often feels very good. Think of punching someone you are angry at, or exacting vengeance on someone that has done you wrong, or getting a young woman drunk and tricking her somehow into sex when she hopes for something more. Your argument from feeling sympathy for others fails, in my opinion.
That is the problem. You view any premise and any argument from it leading to a moral view as acceptable, as "true," because it only has to apply once and tentatively, to you. You don't need it to be strong enough to logically hold together for anyone else under testing and it doesn't have to be rooted in any reality provable to anyone else. That isn't reason. It's preference. The premise of God is an external reality, testable by the simple act of prayer and reading his word.
Why should the thief care whether the victim is better, worse, or the same as him in an athiestic framework? He wants what the other person has and so he considers stealing "rational." When you feel the call to morality, you feel the call to God. Nothing less.
So ... is stealing right or wrong? Please prove your answer rationally.