Jared Diamond has written up a fascinating set of stories about revenge. What I hope is striking is that people can hold completely alien moral codes, and that in primitive societies these are actually pretty dysfunctional.
A couple more examples of alien moral codes. The Chinese attitude to pets is somewhat different. Disgusted? Good. Now think about how a vegan views you. And of course our own culture is not free from change.
So perhaps your own moral code, despite being obviously correct, is actually a result of taking the conclusion your culture requires and backfilling an argument. Sure, it seems to hang together, but at some point there's a little note that definitely does not say "then a miracle occurs". Maybe it's that people can somehow transcend their evolved natures now they have brains. Maybe it's that there's been some kind of weird evolutionary accident that left us all jolly nice people. Maybe there's some kind of moral zeitgeist, whatever that means. Maybe it is that contrary to all reason group selection is actually a strong effect. Maybe being able to understand the motivations of other creatures will make us love them, rather than just letting us exploit them more efficiently. Maybe it's super-rationality a la Hofstadter.
People are nice, therefore <my pet theory> is true. This is progess over "people are nice because God"? Please stop, it's embarassing.
Your moral code has no more foundation than any other, but that is fine, flying is actually pretty straightforward. The proper test of a moral code is whether it results in a society that is to the benefit of its members. It is perfectly valid to pull a whole belief system from your posterior, if it passes this test.
In fact this is business as usual. The 10 commandments are awfully useful. They were probably designed by committee. Same goes for most religious constructs. People choose to believe in them because they work.
You're not going to arrive at the one true moral code by pure reason. You're not going to find it by introspection. Science is silent on the subject. It's not going to be handed to you on a silver platter. You're going to have to damn well design it yourself.
Or wait for some more practical brand of insanity to wipe you from the face of the Earth.
So, um, that's the general outline of the whole "insanity" thing. Obviously it needs a bit more fleshing out. I'm confident that all the various forms of "then a miracle occurs" are indefensible, but each of them is topic unto itself. The idea that other people can have radically different moral codes, and consider them just as natural as one's own, seems to be a common blindspot . I need more examples of these, and more depth to the examples -- how they differ at a fundamental level, and why they still work.
 Two defenses employed here: 1. Labeling beliefs "memes" allow different beliefs to be dismissed as hostile infections. 2. Conspiracy theories allow people's actions to be blamed on coercion and disinformation.