You have to read the whole chapter. The word is Adamah and this is a reference to Eden. There are different interpretations of the Sons of God and the daughters of man. But whoever or whatever they were, they were destroyed in the flood. They are no more. You can look for them but you will not be able to find them. The warning is for people that use their imagination for evil and not good. "
5Then the LORD saw that the wickedness of man was great upon the earth, and that every inclination of the thoughts of his heart was altogether evil all the time." (Genesis 6)
The people that mocked Noah in his day were destroyed. The people who mock him today will be destroyed. AS it was in the days of Noah, so it will be at the coming of Jesus.