Fanciful theories and bizarre interpretations of Scripture lead to assertions that angels “mated” with human females producing half-alien/half-human offspring. This is all false nonsense conjured up by the mind of mystical man. These false teachings mesmerize those with “itching ears” (2 Timothy 4:3-4).
The “Sons of God” identified in Genesis 6:4 were those human males who followed God. They then intermarried with disobedient/heathen women who did not follow God. This is exactly analogous to what the ancient Jews did when they married foreign women, who subsequently turned them away from God. The “Nephilim” were men of “renown,” they were not gigantic monsters or half-alien/half-human beings. Renown simply means that they were men of great reputation. Much like today, when we say that the CEO of a Big Corporation is a man of renown, or that the President of the United States is a man of renown, we mean that they are well and widely known – that they have a wide reputation (and not always a good one). That reputation often conveys some characteristic about those people (for good or bad, for God or away from God).
This false teaching of bizarre alien-like half-angel/half-man creatures then morphs its way into further mysticism and fantasies of man, including UFOs, aliens from outer space, creatures from Antarctica, etc. There simply is no end to the folly and madness of the mind of man!