While I appreciate your obvious concerns here I will try my best (though I’m sure others before me have explained better) to explain my views on this complicated topic.
Also on a side note I misinterpreted your meaning of “genocide” – I thought you were referring to the deliberate massacre of a particular ethnic group, so the book I suggest was about the Joshua Wars.
There is evidence of a local flood that occurred in the Mesopotamian region, around that same time period, I think it’s called the Black Sea basins. As for some interpreters like Hugh Ross, he takes the flood to be, although devastating, not global (some of this can be inferred from the text itself… Inconsistencies in the account about the mountaintops being seen while the dove finds no rest for the sole of her foot… She brings back an olive branch).
I’m not sure about the 8 sole survivors since that seems to describe some level of incest, and not a huge amount of time given to repopulate.
As for the total destruction of humanity, it’s indeed a very difficultly topic. I believe some have pointed out, that according to Genesis he spent 100-120 years building the ark on dry land. That’s quite a big witness, for a lengthy period of time, for the people to repent. Not too mention quite a huge boat that would fit lots of people.
A lot of NT Scholars bring out the similarities between Noah’s situation and that of Jesus. Both preach to the ungodly about repenting lest they experience doom. Both give a large time for those of them to turn from their ways.
But of course, there’s still the high chance of children and babies that could get wiped out by the flood — in Genesis 19 there’s an interesting “debate” Abraham has with God about Him being righteous in his judgement. “will not the judge of all the earth deal righteously and not kill the righteous with the wicked” — it’s a very interesting and powerful chapter I recommend reading.
I think, however, despite such dramatic events such as the flood, people don’t see the “big picture”… God created everyone on this planet, and is all powerful… Over thousands of years he is indirectly responsible for billions of deaths… But many don’t think this way and concentrate on isolated events?
It all seems pretty drab and meaningless… But then Jesus came along and changed things. He (as God incarnate) dwelt amongst us as lowly humans. He was tempted like we are, yet resisted. He died on the cross as penalty for our sins… Then rose again showing us our true potential. He didn’t have to do it… But he did it anyway.
I know if you’re a non-Christian this probably won’t have much affect on you… But it’s the single most important message in the whole Bible — and for believers, the entire world. We probably won’t totally understand all the great mysteries of the Bibles in our lifetimes… But as a Christian we can’t misunderstand the gospel of Jesus Christ. All other doctrinal disputes pail in comparison.
That’s all I have for now, my friend — best wishes