If he thought so then He should have destroyed them Himself. He drowned the whole planet so why not a few thousand men, women and children? He didn't, so the whole story about it being His command is just that. It's just a story that someone could use to justify doing it themselves.
And whether it happened or not is really not the point. It's that people will use the fact that they believe it was His command to justify it. And as we have seen, there are those even within this thread who have said - Yeah, if I really thought it was God commanding me then I'd do it. So there are no guardrails at that point. All you need to commit any atrocity is to believe that God is speaking to you.
That horrifies me. It should horrify anyone.
Well this is what is happening right now, and Jesus in the Bible predicted it. (John 16:2)
Those murdering "infidels" are doing this at this moment, isn't that what you are referring to?
I think the level of evidence of it being God's command would need establishment, and God didn't condemn Gideon for wanting to know for sure what God said, was what God said. He asked for validation. But that is not relevant to Christianity, as we are commanded to love, not kill. (Matthew 22:37-40)
I also think the Old Testament Saints were given a more supernatural view of God. In the historical account they witnessed first hand undeniable miracles of God. This would be a different situation.
Right now, without "God saying so," Russia is killing innocent civilians and children are in that number. The world at large should be more horrified and outspoken, but they seem to me to be complacent. That's not the only example of this going on in the world.
Saul was sent to warn the Kenites, so apparently they were not evil like the Amalekites ("sinful")?
The Amalekites attempted to slaughter Israel on their way out of Egypt, and according to God's plan, the Messiah had to be born into the world to accomplish salvation for the world.
The same God teaches pure love and everything changes after the Messiah has accomplished salvation, and religions that didn't exist then are doing what the Old Testament outlines but seem oddly like copy-cats. There is an epidemic of people who "hear from God" and are getting who knows what from who knows where, interference... personal thoughts... emotional imaginations...
The problem with the query of "would you kill if God said so" is that God was speaking to a nation, in history, using his own people as representatives to bring the Messiah. The purpose being accomplished this same God tells everyone to literally lay down our lives to protect each other and the innocent and leads by example(John15:13), love our own lives not to the death(Revelation12:11), to think of others more highly than ourselves(Philippians 2:3), turn the other cheek(Matthew 5:39), go the extra mile(Matthew 5:41), bless and curse not(Romans 12:14), love and pray for your enemies(Matthew 5:44).
That is a drop in the bucket and a picture of the entire NT.
If someone today, hears anything about killing others in their head and does it, especially in a personal manner, they are obviously in disagreement with God, not agreement.
Now, it can be argued that "back in that time" they were or were not hearing God, but like you said that isn't so much relevant as people using the historical accounts of the Old Testament to justify killing.
I'm sure Hitler had some notion of a "god" or "gods" and that is exactly what it seems to me you are alluding to, is madness characterized by "God said so."
The figure to take note of is Abraham, in that he did exactly what you are mentioning, but then God never actually wanted the man to kill his son on an alter. He stopped him short of doing it because it was simply a test to prove that Abraham trusted God with all his being. A relationship test.
What you are horrified of is on the rise and exists, but Christ doesn't teach that, so posing the question to a Christian is simply asking a person if they are just pretending to be a Christian? Unless they are referring to a hypothetical "if I were Moses/Abraham" example.
If God were to irrefutably show up and tell someone to do something, they are likely to do it, if one doesn't teeter/totter on "Well there isn't a God." Simply put, in the hypothetical situation (for you, that is) that God is absolutely real, and absolutely shows up, you likely (whoever) would do what He asked, such as Moses did, in that hypothetical situation.
If God were teaching that post resurrection (The Biblical God-To kill others for some reason) then there would be a question as to why, if the mission is accomplished.
But He doesn't. Rather He teaches to love. (1 Timothy 1:5) This means such a request would be contrary to His wishes and a direct violation of His commands.
This essentially means we can know without a doubt if we hear a voice in our head telling us to do such things, that it is absolutely not God.