Well, here's the thing, if Hitler told his Nazis to "Love thy neighbor" then what do you think he would've meant by that? Certainly not to love Jews, even though Jews were in Germany and all around them.
You really can't make up your mind what it is you want? Why did you ask for a Christian definition of sin, if you really wanted a Nazi definition of sin. You should be asking fascists this question.
If on the other hand you want a Christian definition, then you need to understand 'neighbour' as the Christians do. Not a Jewish definition, nor a Nazi definition. The only way you are going to get that is to look at the Christian scriptures.
In a sense you are following the legalistic definition that the 'teacher of the law' was trying to get over when he asked 'Who is my neighbour'. Jesus' response was a parable that highlighted the point that your neighbour was anyone who needed your help, which much of the rest of scripture also examined.
It's true that Jesus said to love your enemies, but until that day comes when you rip the OT out of your Bible and tell me you disavow it, I'm going to scrutinize it.
By all means, but be up front about it. Don't pretend you want a Christian definition when you really want to argue with a Jewish definition or with Christians who proclaim that they are obedient to the law.
The authors of the Bible regularly engaged in rape, slavery, and genocide, so I don't think it's unfair to compare them to Hitler. If they had World War II technology, what do you think they would've done to the inhabitants of the holy land?
I'm not sure that the 'authors' regularly engaged in rape, slavery or genocide. How much raping did Moses do? Did Solomon spend lots of his life wiping out other nations? Did Isaiah engage in regular slavery? There is zero evidence for 'regular' actions by any of the authors of any of those things.
Where such things are occurring they are often reported in such a negative way that one can only see them as a bad thing and more often than not God punishes the Jews for such actions... but that then comes back to a Jewish definition of sin, NOT a Christian one, which is what you asked for.
So now I'm confused... are we going with Christ's words now almost entirely? Do you as of this moment disavow the OT?
No, and you should give consideration that there is more than two ways to make use of the OT. One does not have to either embrace it wholeheartedly or disavow it completely. Indeed I don't think any Christian has EVER done either (in the first instance, you might as well be a Jew and in the second you would be a heretic like Marcion).
The real response is to treat the OT like it is meant to be. When it comes to the Law, for example, it is a covenant made between God and Israel. Jesus came and brought a New Covenant (Testament), making the old one of use, but not binding.
When I became a Christian I signed up to follow Jesus, not become a Jew and while the two are not mutually exclusive, it is not required to be both.
It seems obvious to me that a Christian should sell all he has, give to the poor, and wander the world doing good works and preaching the gospel. That's what I would do if I were a Christian. But I would also admit when I'm utterly destroyed in an argument. Perhaps give at least one of these things consideration.
What you would do is not necessarily the same as what another would do. For starters the requirement to sell all you have and give to the poor was given only to the Rich Young Ruler, though many have embraced the same thinking. Nor is it necessary to wander the world doing good works. Jesus only left Palastine to go to Samaria. His total area of travel was less than the size of Wales. From the travels and writings of Paul it is clear that many people stayed put and lived out their Christian lives in their current location.
Perhaps you should give consideration to the fact that you don't seem to know what it is you want. If you really want to argue the points of the OT law, why make up some rubbish about wanting a Christian definition of sin? If you want a Christian definition of sin, then why keep going back to the law when its relevance, at best, is indicative to the Christian, not binding.