The book that the Catholics assembled (they got THIS part from the Jews) said they were around in those days.
4 The Nephilim were on the earth in those days - and also afterward - when the sons of God went to the daughters of humans and had children by them. They were the heroes of old, men of renown.
5 The Lord saw how great the wickedness of the human race had become on the earth, and that every inclination of the thoughts of the human heart was only evil all the time. 6 The Lord regretted that he had made human beings on the earth, and his heart was deeply troubled. 7 So the Lord said, "I will wipe from the face of the earth the human race I have created - and with them the animals, the birds and the creatures that move along the ground - for I regret that I have made them."
8 But Noah found favor in the eyes of the Lord.
It does NOT say the GIANTs mated with the Humans; it merely says they were on the earth. ??? So; just WHO are the sons of God and the daughters of humans??? The BOOK says: Let Us create Man in Our image. So there you get some 'sons of God'; right?? The BOOK also says, in Genesis 5:3-4 When Adam had lived 130 years, he had a son in his own likeness, in his own image; and he named him Seth. 4 After Seth was born, Adam lived 800 years and had other sons and daughters. These things happened BEFORE Genesis chapter 6....
Spiritual sons of God, from the righteous line of Seth. believers in fellowship with Him through confession of the sin(s) of their federal head Adam, repentance from their own, in felowship with The Father and His Son.
Daughters of men, of the line of Cain, clinging to their unconfessed behavior, and bearing the mitochondria of that linem yielding a mixed multitude.
Filtered through the eight few that were saved out of the flood by not being baptized in it.
Angels are spirits, do not have DNA, and cannot procreate with each other or with human flesh (Heb. 1:7). Neither could The God, until He invested Himself into Human flesh, became incarnated, that is; and still did not so far.
If any scripture's plain sense is common sense, seek no other sense.
My opinion, and that of most others who are at rest with my Heavenly Father.