Chapter 2 is rather gloomy reading. It describes false teachers in very explicit terms. Peter refers to them as shameful (v.2), greedy (v.3), corrupt (v.lOa), arrogant (v.lOb), blasphemous and ignorant (v.!2a), beasts (v.!2b), blots and blemishes (v.13), springs without water and mists driven by a storm (v.!7a). They "mouth empty, boastful words" (v.18) but are, in fact, "dogs returned to their vomit" and "sows wallowing in the mud" (v.22). They are truly a destructive lot.
The men Peter refers to here were probably some of the earliest heretics known as "Gnostics". There were various kinds of Gnosticism (from the Greek word "gnosis" — "knowledge"), but the heresy itself essentially was an outworking of spiritual pride. The Gnostics were mystics who were tired of, if not "beyond", the simplicity of the Gospel. They wanted the "deeper" things.
One of the tragic realities of Gnosticism was the dehumanizing of Jesus. Because they saw all material things (including flesh and blood) as evil. They declared it a contradiction in terms that God should become flesh and dwell among us. Jesus, in their eyes, wasn't really human, but some kind of angelic illusion. This, of course, totally destroyed the meaning of atonement — for only if Jesus was truly man, and truly sinless, and shed real blood on a real cross, was He a once for all sacrifice for sin. If He wasn't human, he could never have become "the Lamb of God".
Their view of Jesus was wrong, and, as you might expect, their morality was also wrong. They were characterized by spiritual mysticism on one hand and carnal sensualism on the other. They had "eyes full of adultery" and "never stopped sinning" (v.!4a). They preyed on the gullible and seduced them to their compelling combination of sex and religion (v.!4b).
That's why the chapter is so forbidding. Peter was angry; and rightly so.