What makes one person good and the other bad ?
I don't think the environment has an effect since we can see bad and good in the one same family, many good people are poor and living in bad condition whereas we can see bad rich people living in good condition.
Is it a DNA issue or a soul one ?
Most people are both good and bad on occasions. I consider myself good but I know I have done many bad things in my life.
But given the right (or maybe wrong) conditions, almost everyone can do horrible things.
You honour Muhammed, but, by modern morality, he did many things worse than you or I have ever done. You will justify these that they were acceptable given the context in which they occurred. I'm not trying to make an argument that he did anything wrong, simply I'm pointing out that good/bad is completely contextual.
Most people are a product of their environment, we all like to think that we are exceptional and would behave differently, but most people are not special. By definition, most people are average.
Most white people in Apartheid South Africa weren't active opponents. Most people in American slave states weren't active opponents. Most Arabs in the 7th Century didn't oppose slavery. Most Athenians didn't oppose slavery either.
Yes, some people are just nasty, but most people are products of their environment. Most people would just be average in whatever era or situation they lived in.