“Read for yourself the story of the Biblical Nephilim, the fallen angels described in Genesis 6 and how they descended to Earth and took human wives, who gave birth to a race of demonic giants.”
I also have been taught that the passage saying sons of man married daughters of God referred to fallen angelic beings intermarrying with human women. However, I have done some more study since then and I believe that the sons of God refer to God’s human creation that follow and trust Him while the sons of man are God’s human creation that ignore/forget/rebel/challenge God’s authority. The split became apparent with Cain and Abel. Cain moved away and took glory in his disobedience. He did it “my way”. We are studying Genesis verse by verse and I appreciate the real way our pastor is handling the text. Other passages support this view. Life supports this view, really. It isn’t as sexy as fallen angels theory but that is what I believe. The split in humanity still is apparent between those who believe and trust the Creator of the Universe versus those who want nothing to do with Him or His ways and want to be masters of their own universe.
As an aid to your reevaluation of the above, I suggest you consider Who it was Who called Himself, "The Son of Man"...