This is not a question of what works - that is useless in morality becuase it makes cruelty and non-cruelty equal (the very antithesis of morality). No, Christian moral principles come from God, and are absolute, universal, essential, eternal, immutable; whereas your moral principles are mutable, relative, self-centered, non-essential, and temporal. Night and day.
There is nothing inherently evil about a rationally-derived morality. If the morality promotes survival, the morality will survive. If it does not, it will not. The Golden Rule promotes survival.
Yeah, I'm sure you always consider whether or not your moral decisions promote your survival before you make them. Rationally-derived morality as you described it has no foundation and no standards other than self-interest. It was in Hitler's self-interest to slaughter 6 million jews.
I haven't the time to elaborate right now, but I believe that to be objectively untrue. Customs, traditions, morals, all figure into the survival of a culture. That is why some freepers can be conservatives without attributing their morality to any revealed document.
The majority of people don't want to hurt other people. They band together together, form governments, to protect themselves from psychopaths, who have no inborn inhibitions.
No it doesn't. You don't seem to be grasping the point. Cruelty is self-defeating. Those practicing such "morality" go by the boards relatively quickly. You don't want to be treated cruelly, do you? So, obviously you make a deal with those around you: "I won't treat you cruelly, if you don't treat me cruelly. Live and let live." If you start treating the others cruelly, they're going to gang up on you and eliminate you from the gene pool.
But it was in the world's self-interest to remove him before he came after them. His actions showed the world he was incapable of abiding by civilized conduct (which also predates Christianity) and was a threat to everyone.