Tolstoy said 'All happy families resemble one another, each unhappy family is unhappy in it's own way,' and I think this in some way applies to good and evil, that there are only so many ways that good can express itself while evil has a multitude of expressions. The urge to be self sacrificing, to give to others, to do other good things doesn't have the same appeal as to take what you want even when it's at a cost to others, to trample over people to get your own way; to behave badly when you know you should behave well is often just easier than to do the right thing. Luckily people have people they love and the urge to do evil things is offset by not wanting those people to be disappointed in you, to find out that you're not the person they want you to be and by the fear of the consequences that society needs to impose to curb our desire to be bad.