Divine Command Theory (or objective morality) exists in every religion. It is the idea that a divine command from a god is moral, because the god said its moral. In modern religions (Christianity, Islam, Hinduism, &c) it takes that form because a holy book says God said it was moral.
Rebuttals to Divine Command Theory go way back: Even Plato made one.
"Is the pious loved by the gods because it is pious, or is it pious because it is loved by the gods?"
- Plato, Euthyphro
In Christianity and Islam, the two religions both argue in their holy books that humans are intrinsically evil, their morals cannot be trusted, so they must put their trust in God’s morality to be a good person.
Both the Bible and Qur’an depict genocide, rape, slavery, disowning your family, killing the (alleged) adulterous or gay person, &c. as moral goods when commanded by God. Most Christians and Muslims will ignore the parts of their holy books that depict immoral acts, while simultaneously claiming that the books describe objective morality (hardly any Christians stone to death their unruly children any more).
There are many fails involved with Divine Command Theory.
a) How can a person determine a holy book or its commands are moral if their moral compass is faulty? The answer is usually special pleading (God lives in everyone’s hearts)
b) Secular morals change as societies learn more about working together (slavery is no longer legal in the USA, France, the UK, &c). The Bible has never been updated (slavery is still held as a moral good in both the Old and New Testaments). The argument sometimes given by Christians is that they are “under a new covenant” which suspends all those old Jewish laws for Christians (but they keep those pesky old Jewish laws called the Ten Commandments). If that was the case, and God usually being described as omnipotent, Jesus could have said something like “Thou shalt not own people as slaves.” Instead we have “Slaves, obey your masters, even the cruel ones” and an entire book (Philemon) where the writer begs a master not to punish a runaway slave because he is a Christian. (He doesn’t ask in Philemon to release the slave. The writer is returning the slave.)
c) Objective morality presupposes an agent to propagate those morals. No such agent has ever been shown to exist, or if such an agent exists, it is actually objectively moral.
d) Infinite regress: The objective moral lawgiver exists prior to the "creation" of the Universe. Who created the creator?
e) All societies have moral codes regardless of religious views. No society has ever countenanced murder for example (except some in certain ritualised situations, linked to religious practices fancy that). Theft is universally condemned. People do not need a religious book to tell them these things are antisocial. They figured that out long before religions came along.
f) Circular reasoning: The whole idea of Divine Command Theory is a circular argument. God said it’s moral so it’s moral. The book says anyone who doesn’t believe in the book is necessarily immoral.
g) Free will reasoning: Apologists argue that when a criminal commits a violent act on a person, he or she is exercising the free will God gave that person. Question: If you are mugged or shot, are you exercising free will to be a victim of a crime? Secular morality holds the criminal responsible for his or her action; objective morality holds both responsible.
h) Committing crimes for a higher good: Just down the road from here two years ago, a maniac burst into a Planned Parenthood clinic in Colorado Springs. In the ensuing five-hour standoff (which ended when SWAT crashed an armoured vehicle through the lobby entrance), three people were killed (a police officer, an Army enlisted woman who was also a mother, and a friend of one person who went to the clinic; nine others, four police officers and five citizens were wounded). The man stated he killed in the name of Christ to “save the unborn babies” (one of the women killed was pregnant and at Planned Parenthood for a prenatal visit, not an abortion). He is now held in a state psychiatric hospital indefinitely after the court determined he was unable to stand trial for the murders. The man had previously described the Army of God (Christian terrorists in the USA who blow up abortion clinics and murder people) as heroes. He also screamed “no more baby parts” (a reference to Republican candidate Carly Fiorina in the 2016 Republican Primary race claiming that Planned Parenthood sells baby parts for profit).