Was god justified in killing people in the flood?

The question becomes, does God need a reason for this action? Without warning, the reader is thrust into one passage about his displeasure, and “the Lord said, I will destroy man whom I have created from the face of the earth; both man, and the beast, and the creeping things, and the fouls of the air; for it repented me that I have made them” (Gen. 6:7). According to God’s rhetoric and subsequent justification for his acts, it is his creation; therefore he may do what he wishes with it. There doesn’t seem to be any lengthy explanation, only the simply rhetoric of what amounts to, “I’m God and I can do what I want.”  Unlike in other sections of the OT, there is little reason given, and this makes God seem not only completely misanthropic, but more importantly, a fickle judge who is prone to making snap decisions that cause widespread damage. Rhetorically speaking, the only justification he deems to offer the reader (and presumably Noah and the rest of humanity that he so quickly wipes out) is that since he is God, this is his right.

But is this a valid argument? I suggest it is not. For example, Mankind is always wrestling with the proper way to handle lab animals. We have decided that treating animals so that they experience as little pain and discomfort as possible is the humane way to deal with them. I would like to think that God would consider us more important than lab animals. Additionally, we are supposedly formed in the likeness of god, so we should have similar perspectives. So, is a worldwide flood the most painless way to kill humanity? Actually, it would be one of the most terrifying.

So, is the point for God to show that he can kill us in a terrifying way? The fact that God could kill us all anytime he wants would be the critical point. He would have accomplished the same effect by turning us all into salt, as he did with Lot's wife. Additionally, he would not have wrecked the entire ecosystem that way.

The story is absurd. Actually, the entire bible is absurd, but I shall focus on this one story. God kills all of mankind for sin. However, he allows Noah's family to survive, even though they would have been doing the same sin. How is that justified? If the sin that he killed all mankind for was so terrible, then Noah's family deserved to die as well.

I submit that God was not justified to kill everyone in the flood. Which is good, since it was only a fable anyway.

Since I wrote this, I had a debate with a Christian who posted this statement.

"God does not & can NOT "MURDER". God FORBIDS man to 'murder'.
"The Lord giveth. And the Lord 'taketh' away."

"... we intuitively know that man & God have different prerogatives.
It is inappropriate for men to take innocent life
simply because we are robbing other human beings of a God-given gift,
& we are not to play God in that regard.
But clearly God can play God.
It is His role & He is not robbing when He takes away what He has given in the first place.
It is something that is under His appropriate control.
He can take a life anytime He wants.
Taking innocent human life is wrong for us,
because taking life is God's prerogative, not ours,
which means it is appropriate for Him to do it,
not us,; & He can dispense & retract life whenever He pleases."
- Greg Koukl

God is the Author of life,
the Beginning & the End,
the Alpha & Omega,
in whom we live, breathe & owe our being.
God may take His own."

My response: But god not only kills people, he commands people to kill other people. If he forbids man to murder, then he is inconsistent when he requires that people kill in his name. If god can kill mankind, then he should do so and not make people carry out his dirty work. He killed people in a flood, by turning them into salt or having the holy spirit kill children like the children in Egypt, so he is perfectly capable of killing anyone he wants.