The OP was about Christians who were not around in the OT. But I'll gladly detour for a moment.
You are so right about making excuses for one's faith. It is much easier to do that than have genuine understanding about any intellectual pursuit. That takes work!
I almost hate to say it, but I noticed that you just decided it doesn't matter, instead of honestly looking into the matter with an open mind. Practically speaking, that is no different than making excuses. I don't mean to attack you, but it did strike me as pertinent.
Whether or not one takes the Bible as truth or a fairy tale does not take away the fact that it is a literary work. Like any story, it has characters, a plot, a theme, etc. One thing is certain, a good story must follow a logical course of action. Again, this applies to fairy tales as well as "A Tale of Two Cities." For any literature to stand the test of time, the author must ensure there is a logical story line. That means everything he writes does matter. If nothing mattered there would be no story. So, you see, the things that did happen in the OT matter greatly.
Besides, what you call excuses is actually a knowledge arrived at by a thorough research of the matter at hand. Anybody with a willing mind can learn why the things that happened in the OT happened. Excuses are not required to explain God's plan. It explains itself in the scriptures.
OK. I'm done with this OT stuff. Of course I'll read any reply you may have, but I am still looking for answers to the OP? The essence of the question is, is history filled with heinous atrocities promoted by genuine Christians or by Greek philosophy and Egyptian mythology? We (not everybody of course) claim to be governed by "Judaeo Christian" ethics. I'm claiming that we are in fact governed by the ethical system spawned by decidedly non-Christian doctrine.