Gentile morality

The rabbi opposed the simple teaching that comes from the Gemara in its interpretation of the verse, “And kindness to the nations is a sin.”
It is clear that morality without God, let’s say that pragmatically it can hold up, but its idea – stems from selfishness and an interest in maintaining the human race, and therefore is not moral in the pure sense of the word. For if there is proof that a divine being commanded to behave in a certain way, then it bypasses the philosophical-ethical problem according to which every human law stems from egoism.
In simple words, all humans who have exercised their power over others and robbed them of their freedom are equal in terms of values ​​and morality, including Joshua ben Nun, etc. But God commanded this, and here every religion must logically prove its connection to the transcendent being. I hope that is now clear.