Because I have a person I believe I am and want to be. It’s all about looking at myself in the mirror. Then of course there’s the social contract. It’s very easy to see that the more people that follow the basic rules the smoother life is for everybody. And of course we have enough immoral behavior from people who claim religion to see clearly that being tied to religion doesn’t make a person good. As I said in the other post, if you’ve got the stuff to be a good person you will be with or without religion, if you don’t you won’t.
I understand your views, but I don’t think you understand how inconsistent those views are with the atheistic worldview. You look at yourself in a mirror and apparently “want” to maintain the “social contract” and make things “smoother.”
Why is adhering to the “social contract” a good thing? Why is “smoother” a good thing? Why shouldn’t you do as you please as the fittest, stomping on those you can to become the alpha of your world? Are your fellow atheists doing “evil” to stomp others? Who decides “good” and “evil” and “immoral?” By what standard? Why?
I hope you see my point. Atheistic moral standards are profoundly subjective, with as many moral standards as there are atheists, from complete sociopaths, to people like yourself, who has incorporated the Judeo-Christian moral worldview, at least partially, whether you want to admit it or not.