~MacArthur, "The Battle for Truth, Part 1"
This happens within "Christianity", not just outside of it.
Jud 1:4 For certain people have crept in unnoticed who long ago were designated for this condemnation, ungodly people, who pervert the grace of our God into sensuality and deny our only Master and Lord, Jesus Christ.
2Pe 2:1 But false prophets also arose among the people, just as there will be false teachers among you, who will secretly bring in destructive heresies, even denying the Master who bought them, bringing upon themselves swift destruction.
2Pe 2:2 And many will follow their sensuality, and because of them the way of truth will be blasphemed.
2Pe 3:5 For they deliberately overlook this fact, that the heavens existed long ago, and the earth was formed out of water and through water by the word of God,
2Pe 3:6 and that by means of these the world that then existed was deluged with water and perished.
2Pe 3:7 But by the same word the heavens and earth that now exist are stored up for fire, being kept until the day of judgment and destruction of the ungodly.