Believer says: The atheist cannot condemn a murderous and repressive regime by some absolute standard.
But skeptic says: Well, if a Christian standard is what is meant by “some absolute standard,” the Christian can't condemn a murderous and repressive regime since a New Testament letter by Paul says
Romans 13:1 Let everyone be subject to the governing authorities, for there is no authority except that which God has established. The authorities that exist have been established by God. 2 Consequently, whoever rebels against the authority is rebelling against what God has instituted, and those who do so will bring judgment on themselves. 3 For rulers hold no terror for those who do right, but for those who do wrong. Do you want to be free from fear of the one in authority? Then do what is right and you will be commended. 4 For the one in authority is God’s servant for your good. But if you do wrong, be afraid, for rulers do not bear the sword for no reason. They are God’s servants, agents of wrath to bring punishment on the wrongdoer. 5 Therefore, it is necessary to submit to the authorities, not only because of possible punishment but also as a matter of conscience.
Recap: It sounds as if human government is God’s will for better or worse and so Christians should accept all forms of it.