I mean, all these questions are answered and re-answered in this thread.
But I'll reiterate one part of what you're talking about here.
Matthew 24:38
New King James Version
38 For as in the days before the flood, they were eating and drinking, marrying and giving in marriage, until the day that Noah entered the ark,
Just like today, there were illicit marriages going on.
Let's look at the word "eating" here.
5176. trógó
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Strong's Concordance
trógó: to gnaw, munch, crunch
Original Word: τρώγω
Part of Speech: Verb
Transliteration: trógó
Phonetic Spelling: (tro'-go)
Definition: to gnaw, munch, crunch
Usage: I eat, partake of a meal.
There are 6 occurrences in the NT of this word. All dealing with eating human flesh. Here, in Matt. 24, and the rest is Jesus talking about eating His Flesh.
There are several other Greek words used in the NT to denote what WE think of when we say eating, such as:
2068. esthió
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Strong's Concordance
esthió: to eat
Original Word: ἐσθίω
Part of Speech: Verb
Transliteration: esthió
Phonetic Spelling: (es-thee'-o)
Definition: to eat
Usage: I eat, partake of food; met: I devour, consume (e.g. as rust does).
You don't have to read Enoch to see that the Nephilim were cannibals. We are Told that in Numbers 13:32.
So in Noah's day we had:
1. DNA manipulation of God's Creation
2. Unnatural marriage unions
3. Rampant cannibalism
So Jesus is saying that is going to be the condition of the Earth's inhabitants upon His return. That's why keeping track of how we are mixing species, even with ourselves, is so important.
THAT, was THE sin that caused God to wipe the world clean, and start anew.