Well doesn't the bible say that the Son's of God came into women etc so isn't that already proven by scripture? And also doesn't the Bible say in Revelation that there will be a demonic army unleashed in the end time?
To the second part of that, yes. And I'm familiar with the passage in Genesis about the first part of your post:
Gen 6:1 And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them,
Gen 6:2 That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.
Gen 6:3 And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.
Gen 6:4 There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.
I've got to say you've made me think about this a bit. My understanding was always that this passage was just talking about the propagation of humanity... but since verse 1 says that already it seems kind of redundant in verse 2.
And then, looking at the phrase "sons of God" in the Old Testament, it seems that with the exception of ONE case, "sons of god" always refers to angelic beings.
Hosea has the one exception:
Hos_1:10 Yet the number of the children of Israel shall be as the sand of the sea, which cannot be measured nor numbered; and it shall come to pass, that in the place where it was said unto them, Ye are not my people, there it shall be said unto them, Ye are the sons of the living God.
Not sure my mind is changed, based on the points in my previous posts, but it is something to think about.