God flooded the Earth for the better, not because He wanted to kill his creation. He gave them immeasurable chances turn back from their wicked way, for millionths and millionths of years: children were killed as a sacrifice to their so-called 'god', people committed unimaginable crimes ... people are more than intolerable, that's why God gave the world a 'fresh starts'. If God had been so nasty after all, why would HE bother saving a single family? It's just Noah and his family-- literally only five people out of the whole population that filled the Earth. He cares for every single one of his creation, as it has been proved when God asked Noah to build an arch because Noah and his family ALSO have free will like everyone else, but chose to stay on the right path. He HAD to do this, otherwise, imagine what our Earth would be like if God let those generations continue until today?