Why is so much of the behavior of these false teachers animalistic?
Because what they know is natural, from the energy of the flesh, Jude calls them brute beasts. Their thinking does not go any deeper spiritually than an animal, so their behavior becomes animalistic and they corrupt themselves in those natural things.
Les explains from Jude chapter 10 that false teachers speak evil of things they know not, ridiculing and scorning the truth of God’s Word and setting up their own Bible, so to speak. Their knowledge comes naturally, from the energy of the flesh, as brute beasts. Their thinking never goes deeper spiritually than an animal; that is why so much of their behavior becomes animalistic. As brute beasts, they corrupt themselves in those things. Jude pronounces woe on them because they have gone in the way of Cain, who rationalized from the human side.
But these speak evil of those things which they know not: but what they know naturally, as brute beasts, in those things they corrupt themselves.
More Questions
How do false teachers treat the truth of God's Word?
False teachers ridicule and scorn the truth of God's Word and adopt their own version of the Bible.