I knew this would wind up here. Sometimes I can predict what the critic is going to say so accurately I wonder if I should just play both roles and debate myself. That being said I do sympathize with your point. I will attempt to give a likely or possible explanation. As I have stated I cannot access everything God did when the decision was made and can only go by revelation. He said in the bible that these people had gone completely evil. I mean Jeffrey Domer or Sadam Hussein evil. If you had seen some of the things I have seen in the military then this doesn't seem all that impossible. He said even their thoughts were evil continuously. He spent approx 100 years trying to get them to repent, they refused and taunted the only righteous family on earth. They in effect called God a liar. God did not have an infinate amount of choices. He is voluntarily restricted to acting consistent with covenents and revelation etc..... It could be that he saw what was going to happen if he didn't get rid of the problem and it was horrible beyond imagination. Keep in mind that God is a judge with the power and right to administer judgement. By his standards they deserved death. So he judged and destroyed them to allow a more righteous group to propegate. That's my take on it. I believe it is consitent with the bible and God's nature. Most people only remeber or talk about God's Teddy Bear loving nature which is true. They don't like to think about his terrible wrath that his rightous nature sometimes demands. Like I said I understand the unsettleing nature of his judgements, but that has no bearing whatsoever of his reality. I will also add that if he never displayed his righteous indignation then why would anyone consider the existence of judgement and Hell a reality. I also think he allows evil to witness to the reality of Satan and the (dark side).
Let me just deconstruct this for a moment and address a few of the claims you make.
God did not have an infinate amount of choices.
If god is infinite then he very much does have an infinite number of choices, the god you describe would appear to be the best that bronze age man could envision. FAIL
He spent approx 100 years trying to get them to repent
Wow a whole 100 yrs at a time when people lived for 800 or 900 yrs, he really gave it his best shot didn't he? Especially when you consider that he'd already spent 13.5 billion years getting to that point. FAIL
He said in the bible that these people had gone completely evil.
The entire population that he had created including the unborn had become completely evil in a matter of a couple of thousand years after he created them. Now how do you suppose that happened? Mankind isn't capable of such an incredible transformation, on it's own. There must have been a supernatural force at work for such a thing to happen. Maybe it was satan or maybe god did it? Now since they are the only two possibilities then it must have been god since he created satan and gave him dominion over earth and if it wasn't good ole satan then it was god, either way it's his screw up. Fail
Like I said I understand the unsettleing nature of his judgements,
You see I have to disagree here, his judgments aren't unsettling they are just plain stupid, they reflect perfectly the human condition extant 4000yrs ago when your book was written. Your god in no way presents as an omnipotent omniscient infinite creator of all, look:
It could be that he saw what was going to happen
even you claim that he may have seen the future. An infinite entity can't maybe see the future he is the future, he can change any part of that future at a whim or less. To allegedly destroy an entire planet because he wanted a different future is simply so unbelievable as to make him unbelievable.