What fallacy?

I am an atheist so I invoke the fallacy of unfalsifiability on this one. You make many assumptions which cannot be proven.

Genocide is good if god commands it.

Morality comes from god

What would prove to you that these statements are not true? If there is nothing then these beliefs are unfalsifiable.

You have one sentence which is truely awful. “Slavery is proof of gods mercy because he could have killed them and chose not to”. In my view god does not exist. Let’s say he does exist. I can think of another fallacy. The fallacy of relative privation. You argue that slavery is good because it is better than death. Slavery is not good just because it is less awful than death. Slavery is awful too. In reality, if god exists, then god gave two awful choices, slavery or death, so god is awful.

That sounds like a joke. I can imagine a laugh track being cued up after that line :) This would be distinction without a difference<>.

Answer "None", there is no fallacy. Two points:

1) A related generalised question is whether "I advise be a good X" is equivalent to "I propound being an X"? Common sense says that "I advise be a good prisoner" is not equivalent to "I propound being a prisoner." So there is a distinction introduced by the word "good" and an argument relying on the difference is not fallacious.

2) In point of fact the Bible does not say you have to be a good slave owner. Either the respondent mis-spoke or the Board OP mis-quoted. One thing the bible says is that people are slaves to whatever has mastered them.

I’ve always believed genocide to be a heinous murderous act unless God commands it. In which case it is a noble, even righteous task because God ordered it. Since God is the originating essence of morality even genocide is moral if determined or ordered by him. (William Lane Craig) Thus, the slaughter of Canaanite women and children as depicted in Hebrews was ultimately condoned in the Old Tedtament, as was slavery. Slavery is proof of Gid’s mercy because he could have just as easily ordered their deaths instead.

Even German soldiers of the Reich were absolved from genocidal crimes because they wore belt buckles inscribed with the words “Gott Mit Uns”. And if you’re reading this and not realizing it is absolute parody and sarcasm you should seek out psychiatric help immediately.