Then would demonically possessed men be called "sons of God?"
Rather, what if the expression "son of God" in the Scriptures refers to individually and directly created beings?
I was not a son of God until, in December of 1977, God created me after the image of Christ as part of the New Birth, when He saved me. That new, individual creation, made me a son of God.
Adam was called "the son of God" as a direct creation of God (Luke 3:38), which reference has nothing to do with being born again or regenerated.
The men (and likely the women) in this passage allowed themselves to become possessed by demons and those demons now completely CONTROLLED the actions, et. al. of those men (and women)....isn't that what possession means?....and that fits with the statement in verse 5, that every imagination of the thoughts of his heart was only evil continually. Think about what that is saying....there were no good thoughts at any point in time in that depraved possessed mind....sounds like demon possession to me. I see no reason why demonically possessed (completely controlled)men could not be referred to as the sons of God, because the reference would be to the ones doing the controlling/possessing (ie. fallen angels).
Angels were ALL direct creations of God and therefore ALL sons of God. Angels therefore do not procreate (there are and were (IMHO) never any baby angels, mommy or daddy angels). Angels are also spiritual beings by nature and do not have by nature physical bodies made or designed to procreate. And angels neither marry nor are given in marriage....there is no reason to because they don't procreate. The reference here says they took them wives of all which they chose....that doesn't sound like a God-ordained marriage to me.
God completely wiped that bloody violent world out ("the world that perished") and did imprison those specific demons (fallen angels) that participated in trying to completely corrupt and utterly destroy mankind through demonic possession.
You are correct that Adam was a son of God because He was a direct creation of God. However, all other humans were procreated from Adam and Eve (we have moms and dads, etc. unlike angels). But you are also correct that Christians are sons of God through the regeneration or new birth provided through Jesus Christ. We are indeed new creations in Christ...And praise the Lord for that.
I just don't buy into this half human - half angel thing and never have. It conflicts with to many scriptures in the Bible.