Well, the burden of proof lies with the one making the one making the claim, so you'll have to deliver to validate the claim that arguments for God are just phony excuses. I would say that you would have to invalidate the strongest arguments for God in order to get me to stop believing. In other words, you would have to show me why the world doesn't need a divine being to exist in its state today (or at all, coming to the cosmological argument, which is the strongest argument for God). So, with a thirst for knowledge, I'm quite exited to hear your reasons for rejecting them.
Anyway, your dilemma. I don't think you get exactly the problem with Cain and Abel. I don't think that at any point Abel burned the feed Cain was going to buy for his sheep. What happened was that God didn't accept Cain's offering and accepted Abel's. Cain killed Abel because, as God said in the Bible, "...if you do not do what is right, sin is crouching at your door..." so I would say that Cain probably killed his brother out of jealousy, not out of revenge (which, mind you, is not the right thing either).
So, your problem with the story of Cain and Abel is more of a strawman fallacy than it is a problem. You're finding a problem with a Biblical event that never happened. Now, if you still have problems with the story and still want to justify Cain, we can take the conversation of this dilemma further to the actual problem, but if you, looking at this story, don't see a problem, we can move on to your next dilemma of whether the "bad people" are justified.