A couple of generations ago the culture in the United States was predominately Christian even if many people in the culture were not themselves Christian. Times have changed. Today the culture is predominately secular. In today's culture people have two major worldview options. That is, there are two major sets of assumptions people hold that help them interpret both life and the world, theism and naturalism.
In a secular culture most people, either consciously or unconsciously, embrace naturalism. Naturalism is the belief that the natural world is all there is, there is no supernatural, no God, no soul, no immaterial substances, nothing that cannot be analyzed by science.
Now, if we're naturalists it's very likely that we're also materialists, that is, we believe that everything in the universe, including human beings, reduces to material stuff and energy. There's nothing that's not physical.
But there's a serious problem here. If we are materialists there's no room in our worldview for free will, mind, reason, or objective moral values.
If we're materialists we believe that everything that happens in our brains is the product of non-rational chemical reactions. These reactions are the product of environmental influences that have acted on us all our lives or they're the product of the chemistry of the genes we've inherited from our ancestors. In any case, they determine the choices we make. There's no such thing as a free choice. The laws of chemistry operating in our material brains determine everything we do. On materialism, we're flesh and bone automatons.
Moreover, if we're materialists we believe that our reasoning process is merely the result of the movement of atoms in the brain, but the collisions of atoms are not something that can be true or false. Our reason has evolved to aid in the survival of the species, not to find truth. If truth helps the species to survive that's just a happy coincidence, it's just as likely that error would have survival value. Almost every other species on the planet has survived for eons, after all, without the benefit of a reason that leads to truth.
Since materialism holds that we have no rational mind, just electro-chemical reactions in our brains, it can give us no basis for trusting those reactions to produce truth and thus no basis for trusting what we call reason.
Finally, if we're materialists we have no basis for believing that some behaviors are objectively wrong in a moral sense. Why, for example, is cruelty wrong? If naturalism is true, the most we can say is that the society we live in disapproves of cruelty, but why is that a reason why someone should not be cruel, especially if they can get away with it? Suppose a society approves of genocide, infant sacrifice, torturing children, slavery, or rape, would that make those things right?
On naturalism the term "morally wrong" means nothing more than that which society disfavors but then it doesn't really mean anything at all, unless one has a deep desire to conform one's behavior to societal expectations. It's simply nonsensical for a naturalistic materialist to make any moral judgments of anyone's behavior. On naturalism, the word "wrong," when used in a moral sense, can only mean something of which the speaker disapproves.
The difficulty is that most people, even if they're naturalistic materialists, believe they have free will, or at least live as if they believed it. Most naturalistic materialists live as if they believe that they have a mind, that their reason is a trustworthy guide to truth, and that some things are objectively and profoundly evil. Yet none of these beliefs are consistent with naturalistic materialism.
So, if our worldview leads to conclusions that we can't consistently live with then, if we're a rational person, we should trade in our worldview for one that allows us to live consistently within it.
The best alternative to naturalism is theism, specifically Judeo-Christian theism, the belief that there is a personal, supremely rational and good being who created us and endowed us with free will, reliable rationality, and whose nature serves as the objective standard of moral right and wrong.
Indeed, it's very difficult to live consistently with any other set of assumptions.
