God did foresee human degeneracy. Revelation 13.8 says that it was known before creation that Jesus would have to be crucified for the sins of humanity. Why would God create then? The only way to have more children is, well, to have more children. Some will love you, some will not. It is the risk inherent in love. Love must be chosen, not forced.
God didn't "get mad." God is the source of wisdom and the center of order (Gn. 1), but Adam and Eve decided to declare themselves as their own wisdom and the center of order. The rest of Genesis 3-11 shows how misguided they were along with how tragic such a perspective is. Humans ruined what God had ordered, and Gn. 3-11 is the story of what the world looks like under human wisdom and order: hopeless corruption and suffering. God put in development a plan to restore what was marred. The flood story is one of righteousness. From the very start we have a contrast of depravity vs. righteousness (6.5-8). The point is not “Is God murderous?” but will his righteousness do what is demanded of righteousness, or will he cave?
God doesn't give up on us no matter how badly we act. But when our badness gets to a point of no return, God has to act or everything will be lost. The reason God acts so extremely is because it's the only way to save that which is lost.
People are free to act in whatever way they choose. God watches what they will choose, and it's horrible.
Now, just for full disclosure, I don't view the Flood as a global phenomenon, but rather as a regional judgment on the guilty people. Universal language in the ancient world was common as an expression of God's work. John Walton writes,
"The rhetoric of universality was a common literary and theological device of the ancient world: “Sargon conquered the whole world”; “All the nations came to buy grain from Joseph in Egypt”; “And they killed every man, woman and child.” The rhetoric of universality was especially common in situations of cosmic catastrophe: “All the cattle died”; “the sun, moon, and stars fell from the sky.”
God foresaw human degeneracy. Genesis 3-11 show us the need for the covenant that God announces to Abraham in Genesis 12, and the rest of the Bible shows how God develops the covenant to redeem people and save them.