Can angels marry humans?

Question: What is Genesis 6:1-4 talking about when it speaks of sons of God marrying daughters of men? Is it talking about humans marrying angels or of Seth's line marrying Cain's descendants? Answer: Genesis 6:1-4 When men began to increase in number on the earth and daughters were born to them, 2 the sons of God saw that the daughters of men were beautiful, and they married any of them they chose. 3 Then the LORD said, "My Spirit will not contend with man forever, for he is mortal; his days will be a hundred and twenty years." 4 The Nephilim were on the earth in those days--and also afterward--when the sons of God went to the daughters of men and had children by them. They were the heroes of old, men of renown. (NIV) The term 'sons of God' is used in Scriptures of both man (Romans 8:14,19, Galatians 3:26, 1 John 3:2 KJV) and angels (see Job 1:6, 2:1, 38:7 in most translations except NIV). There is no indication in Scriptures that angels can have sexual relations... quite specifically God says that they do not marry (Mark 12:25, Matthew 22:37). Granted theses passages speak of heavenly angels, but it appears that they were created without the need/ability (see also Luke 20:35-36), so there is no reasonable extension to say that fallen angels acquired it. You have to read a lot into Scriptures to say that this references angels, even fallen ones. Because God determined that the Messiah would come through Seth's line, and Noah (the only righteous man left on earth [Genesis 6:9]) was his descendant — who God foreordained would be the one whose descendants would repopulate the earth, it could be argued that the 'sons of God' were descendants in Seth's line whom were intermarrying into godless lines [ie. of Cain]. BUT, again some has to be read into Scriptures to get there, including that Cain's descendants were somewhere banned from marrying any of Adam's other descendants [which is not stated in Scriptures]. This is not as great a stretch as the first speculation about Angels though. Since Cain "went out from the presence of the Lord (Genesis 4:16)," it makes sense that his offspring would be godless, not knowing the Lord. More directly 'sons of God' would reference all who followed the Lord with the implication that 'the daughters of men' were of those who did not. God always was opposed to mixed marriage [See 2 Corinthians 6:14, Deuteronomy 7:3-4, 1 Kings 11:1, Ezra 9:1-2] and it would be no surprise that consequence would result [Genesis 1:3-4]. The passage also can be directly understood that because man was living so long, they were taking multitudes of women as wives. Therefore God was limiting their life span to 120 years (Genesis 6:2). This is the most direct sense, without reading extra in. Proverbs 29:16 says "When the wicked increase, transgression increases" (NASU). God was limiting that amount of transgression by limiting the number of offspring [image how many kids you could have with multiple wives in 900 years!]. Some Bible passages, without other clarifying texts, are always more difficult to understand, yet we must always tend to lean towards the most direct sense of any passage. Reading in, is always dangerous.