Spot on. And the real problem is this: in a materialist world—assuming, for the sake of argument, that materialism is true—reality itself would be sociopathic. Look at nature: survival of the fittest, might makes right, predation, even cannibalism. Nature is indifferent, ruthless, and morally blind. In a purely materialist universe, a human sociopath wouldn’t be deviating from reality at all; they would simply be aligning themselves with the way things actually are, rather than pretending that anything truly matters when, ultimately, it doesn’t.
Which is why the reality of God, and the historical resurrection of our Lord, is so crucial: it is the only way the universe can possess inherent meaning. It is the only way for life to be more than a painful rat race toward oblivion. It’s the only way for love to actually make sense and being something more than a word indicating a biochemical reaction.
I think your reasoning makes the issue a bit too simplistic, idealistically black-and-white. Maybe built on an arguably valid claim but leaving out much that may complicate the practice.
As a Christian, I can accept that God is the source of objective morality. Those who do not have the same faith would disagree, which makes the answer somewhat subjective, based on the axioms of the worldviews.
God did not write a detailed guidebook about His morality. We have the biblical scriptures (canon) but these scriptures are not a systematic presentation about doctrines and morality. Much of the scriptures are told in the form of stories, so that the actual lesson needs to be picked and interpreted from that story. What makes the task more difficult is that the stories tell happenings in an environment (society) that was ancient compared to modern rules of morality. That leads to subjective interpretations that may or may not be accepted by the wider community of Christians.
The problem is not that the morality given by God is wrong. Our imperfect and often misunderstood interpretations may just lead to actions that the later generations condemn as wrong. Two examples are the violent crusades or what was done to ‘heretics’ during the Reformation and counter-reformations. During the period of Reformation, all main parties (RCC, Lutheran, Reformed) tortured and killed people just because they did not agree with all the interpretations of the dominant group. Those who did not do take part in the killing (anabaptists and other non-violent groups) were persecuted by all the main parties as ‘heretics’.
At the level of actions, the groups showed that human life did not have much value and the ‘heretics’ had no human rights. They were sometimes treated worse than animals, by people who claimed to represent and follow the will of God.
We can hardly get rid of the subjective part in our morality, even when we try to follow a morality that we believe is objective.