Christians, if you follow the bible, you realize there would be mass genocide?

You have to read the Bible in context. Know that if we choose evil and reject God, then we forfeit our own existence. God is the Source of Goodness, Truth, Love, and Life. He alone has created us and He is the One who holds us together. If we deny the One who is providing us with Life, then we cannot live. God desires that we all would live and choose Him. However, the Bible tells us that there will be many who will not. If God didn't flood the earth and start over with the only Godly group of people left, then no person today would have salvation. God wants us to point each other to the only Source of Life, which is Him. We exist because He thought of us. None of us merited being created, nor do we deserve to be kept alive. The value that we have is based solely on God's love for us and He has placed such a high price on us because His love is great.