That is a totally false doctrine. When men began to call the name of the Lord, that was more than a thousand years ago before the flood, Gen. 4 and 6 are NOT in the same context. Don't take my word for it, count it yourself how many years and generations between Seth and Noah. At the time of the flood, everyone on earth was extremely wicked except Noah, so wicked that had grieved God. God doesn't drown his own sons and daughters in a Flood, he loves them and cares for them. Also, just because someone calls upon the name of the Lord doesn't mean they're holy and righteous.
Not everyone who says to Me, ‘Lord, Lord,’ shall enter the kingdom of heaven, but he who does the will of My Father in heaven. (Matt. 7:21)
Also, don't throw Matt. 22:30 at me, you once again forgot the setting - IN RESURRECTION. Was anybody in Noah's days in resurrection? And even though angels don't procreate, MEN do; angels appeared as men, therefore copulation with them is possible.
Now the two angels came to Sodom in the evening, and Lot was sitting in the gate of Sodom. (Gen. 19:1)
“Where are the men who came to you tonight? Bring them out to us that we may know them carnally.”(Gen. 19:5)