The moral argument is one of the most powerful arguments in favor of Christianity because, as William Lane Craig puts it, "it hits people where they live". We all have a natural sense of right and wrong, and even those rare (yet consistent) atheists who say there is no actual right and wrong can be seen internally cringing when they say it. The trouble is, they are being entirely consistent with their atheistic worldview when they deny the existence of morality.
But most Evolutionists don't want to go that way. They know charity is good, they know theft isn't. They know marriage is good, they know rape is bad. They know it's objectively better to talk through your problems than to throw your fists at the first person who annoys you. Being sinners (as we all are), they may not have a perfect understanding of morality, but they at least know there is morality. The problem is, within Evolution, they cannot justify it.
"But Evolution isn't about morality!", they reply. Well, in one sense, they're right. However, Evolution has implications on morality because it has implications on who the moral legislator is, if one even exists. See, when you want to assess the legal implications of your actions, it's important to consider which government has jurisdiction over you. Take, for example, the question "is weed legal?" For me as a British citizen living in England, the answer is no. Cannabis is a class B drug, which means it is illegal to produce, sell, or use. Doing so can result in an unlimited fine and up to 5 years in prison. In California, however, weed is 100% legal.
Without legislation, it is illogical to even ask "is weed legal?" In order for a thing to be legal or illegal, there must be some kind of legal system in place to define it. If such a system does not exist, weed is neither legal nor illegal. In the same way, in order for something to be called good, evil, moral, immoral, right, or wrong, there must be some kind of legislator to define it as such.
Furthermore, this legislator must possess certain attributes. It must be specifically concerned with human behavior, otherwise its laws could not apply to us. It must be intelligent, otherwise it could not institute, nor enforce such laws. It must be omnipresent, otherwise its laws would have a jurisdiction limit. It must be eternal, otherwise its laws could pass away. It must have some claim to authority, otherwise what makes its preferences greater than our own? In other words, in order to say morality exists, we must believe in a god of some form.
Without question, the Triune God of the Bible fits this description. As the Creator of this world, and the Author of its every natural law, He has every legitimate claim to authority. He is eternal; there was never a time when He did not exist, will never be a time when He will cease to exist, and He does not change. He is omnipresent, all things dwell within Him, for lack of better description. He is omniscient, knowing not only what He desires, but also knowing how to achieve those desires. And of course, He is concerned with human behavior, not only as our Creator, but also as our Commander in Chief.
The problem with Evolution is that it erroneously declares that none of the above paragraph is true. God has made His creation process quite clear, and it is nothing like Evolution. If the Bible is true, Evolution isn't. If Evolution is true, the Bible isn't. Indeed, this is the very reason Evolution was made up. But if the God of the Bible isn't the moral legislator, who is?
In Evolution, this is somewhat open to interpretation. Evolution may justify atheism, but does not necessarily require it. It does, however, limit the options. Some compromisers choose a senile version of the Christian God. That is, they believe He exists, but they degrade Him to such a level that they may as well believe He's the cliched old man on a cloud. These versions of God can err, or even lie. But when you degrade God to a human level, you bring His trustworthiness down to the human level. If you can't trust His word in one area, why should you trust it in others? If He's wrong about the origins of marriage, maybe He's wrong about sexuality in general? If He's wrong about the origins of human life, maybe He's wrong about the value of human life? If God can lie, how can we say lying is wrong? Put simply, compromise on one area of scripture leads to compromise in others, and we become our own gods.
You could also justify other gods, such as Allah. He is so deceptive that Abu Bakr, whom Muhammad had guaranteed Paradise, is reported to have said "By Allah! I would not rest assured and feel safe from the deceit of Allah, even if I had one foot in paradise." (1) In the Qur'an, Allah brags about being the best of deceivers, even to the extent of making it seem Jesus was crucified though He was not. In other words, Allah is such a schemer, he is directly responsible for the rise of Christianity. But this, once again, leads to the problem of god being untrustworthy. A god that explicitly brags about how good he is at tricking people is not a worthy source of information. If you can't trust his word, you can't trust him to tell you anything, much less how to live your life.
We could go on and on about adding gods to Evolution, but ultimately, there are no gods, unless they are so obscure as to have escaped the notice of just about every apologist in the world, that are consistent with Evolution, able to provide morality within such a system, and can be reasonably believed in and defended with the available evidence. This is why Evolution and atheism, while not inextricably linked, are common bedfellows. As Will Provine put it, "As the creationists claim, belief in modern evolution makes atheists of people. One can have a religious view that is compatible with evolution only if the religious view is indistinguishable from atheism." (2).
All of this means that whether Evolutionists like it or not, Evolution has implications about morality, because it has implications about where morality comes from. Therefore, it is entirely legitimate to challenge Evolutionists to justify morality within their belief system. If they can't do it, they are trapped in an inconsistent worldview. And what do you do when your worldview is inconsistent? You fix the inconsistency. You either reconcile the two seeming contradictions (which, for Evolution and morality, cannot be done), or you find the erroneous element and cast it out.
So, Evolutionists, which is the erroneous element in your worldview? Objective morality, or the inherently atheistic creation myth? You could simply say that moral laws don't actually exist. That is cringey, of course. Try saying out loud "there is nothing objectively wrong with kidnapping and repeatedly gang raping a 2 year old girl, I just don't like it". Writing that sentence out makes me feel quite light headed and I don't believe it, so I can't even imagine the internal struggle you feel if you try to actually be consistent with your Evolutionist worldview by affirming it. But the more logical, and certainly less detestable conclusion is that Evolution is wrong, and you know it instinctively.
The challenge is legitimate, but if you're committed to Evolution, it's unbearable, as it leads to one of two intolerable conclusions. The first conclusion is intolerable because it denies common sense. And for once, I actually mean common sense; even a literal psychopath has some concept of right and wrong, as is shown by the fact they know when they have been wronged. Everyone cries for justice, even if they have a twisted sense of what justice is, and so the fact that Evolution means justice is as subjective as our favorite ice cream flavor is simply intolerable.
But the alternative is just as painful, because it is humbling. Not only does it necessitate that we are subservient to a Holy God, but also, we have fallen short of His Holy standard. We don't get to just do what we want, but we have done what we want, and therefore, we are due a fate worse than Evolution. We are owed death.
Here's why that's a better alternative: God doesn't want to condemn us. Instead, He sent His Son to live as a man, never once violating His Holy laws, yet suffering the penalty nonetheless. The punishment Jesus suffered was due to us, meaning the reward due to Him can be ours. The cost has been paid, the only job we now have is receiving the gift. How? By faith. All who repent of their sin, confessing Jesus as Lord and believing He rose from the dead, will be saved. The choice is entirely yours. Live an inconsistent lie, or accept the free gift from the Way, the Truth, and the Life.
References
1. Khalid Muhammad Khalid - Successors of the Messenger, translated by Muhammad Mahdi al-Sharif [Dar al-Kotob al-Ilmiyah, Beirut Lebanon, 2005], p. 99
2. Provine, Will - "No Free Will," in Catching Up with the Vision, Ed. by Margaret W. Rossiter (Chicago: University of Chicago Press, 1999)