Haven't you read it?
Try the flood, just for example: Were there no minors in Noah's day? No infants and children? For what "justice" were they slaughtered by God's rain? How about the first-born of Egypt? Were they all adult, and therefore responsible for their own crimes, or were any of them children? If God had an argument with Pharaoh, where's the "justice" in killing the children of Pharaoh's helpless subjects? Were there no children among the Canaanites who God ordered slaughtered (or in the case of virgin girls, "take(n) for yourselves")? What is "just" about killing a virgin girl's parents and brothers, and then taking her home for your own "purposes?"
It never ceases to amaze me that Christians can't look those details in the face and ask themselves, "is this a just God?"
God created all things, including us humans and we rejected Him and we are told that the inclinations of our heart were only evil from our youth. God has a right to wipe out everyone if He so chooses, and to keep some alive if He chooses.
This, it seems to me, is not the final judgement and is not meant to be 100% just for every single person.
God did the flood to accomplish His purposes on the earth. A world that is evil in it's heart all the time is not going to pull itself up to a higher plane of existence. Things imo would just go down hill more.
The final judgement is a different thing however and God will judge each person separately and apply justice and mercy as He sees fit.
It is the same with Egypt. God wanted to judge the whole land for what they had done, and yes the innocent suffered.
With God as the King of Israel God was seeking also the good of Israel and to give brides (not sex slaves, as you seem to imply) for all the men.
As King God could have said to kill all of the enemy and drive them out of the land but you judge God as evil for saving some of them alive.
It is not easy at times to look at things from God's pov but to get a better picture of God, that is what you need to do.