Religion offers the only objective moral standard available. Whether secular humanists or atheists are willing to accept it, their moral beliefs are formed and guided by religious principles. In the case of those living in Western societies, Judeo-Christian principles. The same also goes for nominal Christians who excise much from the holy book to allow their religion to conform to their worldly beliefs and preferences. They still operate upon religious beliefs, regardless if they realize it or not. There is no moral basis for outlawing murder apart from religion. The argument from secular humanists and atheists to outlaw it is entirely utilitarian. Big surprise that the countries which have attempted to divorce religion from their systems are the same ones in which we see enhanced efforts by the state to help those who offer little or no utility to euthanize themselves, the ones that have the least restrictions on abortion, the ones that offer children more opportunities to permanently damage their bodies. When human life cannot be sacred, and there is no "sacred" in secular humanism or atheism, anything is possible and anything is ultimately permitted. The 20th century is a catalog of mass genocides and the murder of dozens of millions, perpetrated by those who believed they weren't accountable to any higher power. David Berlinski once said to an audience: "I have in front of me a rather remarkable button. If you should press it, yours will be untold riches and everything else you desire. And the only consequence to pressing it, beyond your happiness, is the death of an anonymous Chinese peasant. Who among us would you trust with this button?" Berlinski is a self-describe agnostic, by the way.
Now I ask you, how would we construct a justice system that is moral without a foundation in religious principles of some sort? If you or anyone argues that "The Golden Rule" shall govern it, then I will ask, as I always do, "Why?" Why is it wrong to harm someone? Upon what basis do you conclude that, apart from religion? If the argument is, "I won't hurt you so that you won't hurt me," then that is a consequentialist argument, not a moral basis. And what of those times when I or someone else is completely secure and unthreatened by anyone? Is The Golden Rule inoperable or out the window in such situations? And where does this idea come from that you or I have an inviolable right to our own bodies and lives? By what standard do secular humanists or atheists make this claim? Why should human life be elevated over the lives of other living beings or organisms in secular humanism or atheism?