When reading about giants or any scripture that hints of aliens. You need to just think for a while on the reason mankind needs a Savior and God's hand being on all creation / all creation being good.
Mankind is accountable for sin because of their intelligence levels. These giants, if they were a different breed of man and were once babies, God who is impartial would have to include them in the plan for salvation, not separate them. So, I cannot believe, just on it being illogical and conflicting with much other scripture, that there were giants as a separate race. The best I can fathom is that in an evil society demonic presence would be rife. They could probably take on the form of some man given the opportunity by God. I can agree that some humans were larger then others.
But with all this said the fact remains that the flood came upon mankind because of their wickedness. Just as Sodom, they were wicked continually and had no desire of ever repenting. Gen 6:5 the Lord saw that the wickedness of man was great in the earth, and that every intention of the thoughts of his heart was only evil continually.
My friend...Jesus came to save man, humans. He did not come to save fallen angels or their offspring.... All creation may be good, and it is, but the corrupting and mixing of that creation is not...God's intent was everything after it's own kind....
Genesis 1:25
God made the beasts of the earth after their kind, and the cattle after their kind, and everything that creeps on the ground after its kind; and God saw that it was good.
Genesis 1:11
Then God said, "Let the earth sprout vegetation, plants yielding seed, and fruit trees on the earth bearing fruit after their kind with seed in them"; and it was so.
Genesis 1:12
The earth brought forth vegetation, plants yielding seed after their kind, and trees bearing fruit with seed in them, after their kind; and God saw that it was good.
Genesis 1:21
God created the great sea monsters and every living creature that moves, with which the waters swarmed after their kind, and every winged bird after its kind; and God saw that it was good.
Genesis 1:24
Then God said, "Let the earth bring forth living creatures after their kind: cattle and creeping things and beasts of the earth after their kind"; and it was so.
Genesis 6:20
"Of the birds after their kind, and of the animals after their kind, of every creeping thing of the ground after its kind, two of every kind will come to you to keep them alive.
Genesis 7:14
they and every beast after its kind, and all the cattle after their kind, and every creeping thing that creeps on the earth after its kind, and every bird after its kind, all sorts of birds.
Fallen angels perverted creation by not keeping to their own kind...The offspring is not after the kind, angel...nor is it after the kind, man, but a vile mix of the two. Not human....No salvation. It is in the Word...
Now you think about it....If there is salvation for Nephil, why is there no salvation for the fallen angels?