I've read the whole book; it's not that long. The version that I have did not say any of the above. Methinks these guys didn't understand what Enoch was describing.
1. Enoch describes, during the period before the Flood, how the world became more and more corrupt, which led to God deciding to send the Great Flood.
a. Enoch describes how God allowed angels to be tempted by women (and a lust for power) and choose to leave heaven to become fallen angels. Enoch does not say WHEN the angels fell by this temptation (i.e. before the world was created or after). Enoch also does not mention lucifer as part of this group, so those angels who were cast into hell by St Michael before the world was created were a separate group that "fell" from heaven.
b. Those angels who fell by lust for women/power were given very specific names by Enoch, as well as descriptions of their powers and interests.
c. The angels who fell during Noah's time had children by way of witchcraft, which produced the Giants/Nephalim.
2. The descriptions of the fallen angels who "taught men to sin" is not accurate. What Enoch describes is that these angels gave to those men/women who worshipped them the knowledge of all sciences, technology, metallurgy, chemistry, astronomy, etc. Before the angels came into the world, the world revolved around farming. The angels taught evil men how to do the following:
a. Find, develop and use metals for weapons, technology and Jєωelry
b. Find, develop and use herbs for medicine, potions and poisons
c. Find, develop and use chemistry, biology, etc (all modern sciences) for power, money and war.
d. All of these things led to luxuries, sinfulness and war
Scripture also tells us that all of mankind was "corrupted" but that Noah was "pure in his generations". This leads one to suspect that animal/Nephalim/demonic corruption (i.e. genetic manipulation) was also happening. As one guy argued, Satan wanted to corrupt all of mankind's gene pool so that Our Lord couldn't be born. This is a strong argument and fits into what Scripture implies here.
Also, many Church Fathers are very explicit when they say they believed that the Giants/Nephalim were, in fact, demonic/human hybrids.
Yes, while I've not read the entire thing, I read the first sections of it, and Enoch was clearly talking about the fall of the Nephilim or "sons of God", aka the Watchers. One Church Fathers said that they were sent by God to help guide and direct men. Book of Enoch did NOT say that this was the same as the first or original fall of the angels, nor did it say that this was the FIRST time men fell into sin, but that these fallen Nephilim taught men all manner of sinful things.