Secular morality can actually explain WHY it's wrong.
So why is it wrong according to the secular worldview, that is, if this world is nothing more than a product of astronomical random chance?
There is no wrong or right in the Atheistic worldview, because wrong and right demand a moral absolute. If you say there is moral absolutes, then who or what defines them? If you say it is for the good of society or does no harm, you are back to the original point. Moreover society has defined things in the past that are evil by God's definition as good things (e.g. late 1930's Germany and the genocide of the Jewish people), so society is no absolute standard of morality.
Whereas the "divine morality" proponent can only say "because god says so".
Since is God is the perfect, holy and righteous Creator of all things, and since mankind is created in the image of God, life is sacred, all life is sacred, and violation of one's life either through murder, lying, theft, adultery and anything else God has defined as unlawful, that is the absolute moral standard.
You may choose to reject God's word, but that has no effect on His truth or that He is the Creator of all things and that He is the Just Judge of the universe, before whom you will one day stand and give account for how you violated His perfect law.
The "morality" you refer to isn't morality at all. That's just obedience to a perceived authority.
Not merely perceived, but actual, no matter how much you reject it.
"god says so", is not a grounding nore a reasonable justification.
It is, again, just mere obedience.
Same point again.
So, slavery is okay, genocide is fine, infanticide is fine, public stoning is a-okay, killing gays is okay, burning witches is okay,...………...
Context matters. We are not ancient Israelites, in that place, for that people for that time.
The Bible never calls slavery a righteous act for all people of all time.
The Bible never calls for genocide. God executed divine justice against a wicked, idolatrous and immoral people, and God uses means to carry out His justice.
The Bible never calls for infanticide. Again, God executed justice. Moreover, God, being the sovereign and holy Creator, has the right to do with His creation as He chooses. You don't get the right to hold God on trial in your blasphemous courtroom.