If you look at the human race throughout all of history, and spanning the entire breadth of the planet-- every culture which has ever existed, has had some notion of both good and evil. To me, this is sufficient proof as to the existence of both good and evil. Granted, there are social variations, which account for the 'social norms' mentioned earlier, but the core concepts good and evil seem to be pretty universal. But, most importantly, the most pernicious type of evil is that which is carried out in the name of 'good'. This blurring of the lines, I believe, leads some to the denial of the existence of good and evil. Just my 2 cents.