A key (and tragic) deficit in human reasoning is belief that mankind is not capable of governing himself free from self-forged iron shackles of either mythological deities who know all, see all and who spectacularly punish mistakes of the species or god-like men such as kings appointed to rule by command of said mythological deities.
The way one determines right from wrong (in the absence of any god's wrath) is to identify and differentiate between those actions which harm the continuation of our species and those which benefit it and encourage its proliferation.
For instance, abortion—even without the dusty presence of ancient deities—can be easily identified as morally wrong; the act of abortion—mass abortion in particular—severely reduces the number of humans available to procreate and continue our species. Thus, and without any inclination toward deity worship, the act of abortion is provably, morally wrong. It is the same with issues such as mass homosexuality, mass transgenderism and euthanasia as a societal policy: all three aforementioned philosophical perversions severely detract from the capability of our species to reproduce, perpetuate and survive—all without need of deity worship or mention.
Harming children in any way, be that harm physical or psychological, is super antithetical to the continuation of the human species. War, also, is against the logical means and natural progression of our race other than in those few true instances of war for national defense, a situation which is historically so rare as to (almost) have never arisen.
Murder is also antithetical to prosperity in general, unless one sets out to be a madman, and unless one is killing in self-defense. Either way, murder removes warm human bodies capable of reproduction and continuation of our species.
Living by a good moral code requires neither genius nor belief in a god; only love for oneself and our species are necessary.