I believe in the moral principles. I don’t have to believe in God to believe that to lie is wrong, to steal is wrong, to kill is wrong, to cheat is wrong - most people in the world agree on those despite different religious beliefs.
Why are all those things wrong?
If we are just the product of random, naturally directed chemical processes, there is absolutely no reason to treat your fellow humans with any sort of “fairness”, up to and including taking their life.
Like I said, you might just as well be angry at vinegar reacting with baking soda.