Regarding evil DNA, I don't think that's quite what happened. I think it just means that after creation, people began to multiply and have daughters, and the men saw how attractive they were and 'married whoever they wanted', whatever that means. The language is similar to when Eve saw that the forbidden fruit looked good to eat. Looks like they married women for their looks rather than other qualities, so that their children grew up without the fear of the Lord. We are told that the Nephilim were also on the earth at the time when God sent Israel into Canaan to expel the people from it. The people of Canaan practiced the kind of immorality described in Leviticus 18, which caused 'the land to vomit out its inhabitants' because it was defiled (v.25, 28). You could say that the flood was a different mechanism for achieving the same end, on a universal scale.
2 Peter says that the present heavens and earth are reserved for fire. Whether this is the literal burning up of the earth or a symbol for eternal separation from God, it shows that the Flood was a picture of a universal judgment still to come, from which one can be saved by faith in JC.
I'm sorry but this is really a load of mumbo jumbo.
People have beaten me too it but I find it nigh-on impossible that people still believe this myth in today's day and age.
Let's not mince words: if the story of the Flood is to be believed, God is a moral monster. To say his response to the alleged wickedness of humans is disproportionate is a gross understatement. Moreover, God engages in conduct that we would expect from the worst dictators, namely collective punishment that sweeps in the innocent along with the guilty. Children, presumably, were among those drowned (unless we assume that wicked adults had no offspring) as were most all of the animals, who bore no responsibility whatsoever for the misdeeds of humans. Intentionally drowning a kitten is conduct we'd expect of some psychopathic juvenile, not a loving deity.
Ronald A. Lindsay