The resultant hybrid offspring from mating of angels with the daughters of men, per Genesis 6, REALLY HAPPENED. There's quite a bit of Old Testament Scripture that describes their great PHYSICAL stature too, showing they were a hybrid race.
Isa 26:14
14 They are dead, they shall not live; they are deceased, they shall not rise: therefore hast Thou visited and destroyed them, and made all their memory to perish.
KJV
That Hebrew word for "deceased" (rapha) in the above verse is one of two places the King James translators failed to bring the name Rephaim into English, a proper name for a group of the giants described in Old Testament scripture.
According to God's Word, all born in the flesh that have died will have a resurrection, even the wicked. But NOT THOSE in that above verse. It specifically says, "they shall not rise". That means that verse HAS to be pointing to a hybrid giant race.
God did not create those hybrids. A group of fallen angels ("sons of God") saw flesh women, that they were fair, and took wives of all those whom they chose. That means they married flesh women and had sex with them. They left their heavenly habitation is what the Book of Jude says; other than that, I don't know how... they physically mated with flesh woman, God knows. And we are expected to believe it happened just like the Scripture declares.
And just to let us know further in Genesis 6 that an actual tainting of flesh seed is what was going on with the Nephilim, God said that Noah was "perfect" in his generations. The Hebrew word for "perfect" there is the same Hebrew word used for the sacrificial purity of animals required per the old covenant sacrifices. So it is directly referring to Noah having kept his literal flesh genealogy intact, and not mixed with those hybrids.
The Genesis 6 Scripture shows there were TWO irruptions of that mating of the fallen angels with flesh woman, once before the flood, and then "also after that". It also says those offspring of giants were "men of renown", meaning literally, 'men of the name', or legend. What legend? The legends of mythology of gods walking upon the earth that is in the ancient histories of many cultures.
Even the North American Indian culture mention that history of a hybrid race giants of great physical stature once upon the earth, running along with buffalo, grabbing one, tearing its leg off and eating it while continuing to run along with the buffalo (from Buffalo Bill's autobiography from a Pawnee Indian that brought a huge femur bone into the camp to show him. A doctor present on the expedition pronounced it as an authentic human femur bone, but larger than one of normal man). So-called Indian burial mounds have discovered many skeletal remains of humans over 11-12 feet tall.
It is secular science that refuses to accept the mention of an actual race of hybrid giants once walked this earth. Well, they also refuse many other events written of in God's Word, like the Genesis creation by God, the resurrection of Christ, and many miracles recording in God's Word. So who in the world that claims to be a Bible-believing Christian would ever side with those unbelieving scientists who are way... behind in understanding God's creation, and even the old world when Satan first rebelled?