Just the thought demonstrates their philosophy, that they don't believe the Bible is the first place. They think the Bible was just made up by people, therefore, they think they can change it to whatever they want. It also reveals their philosophy that religion is just a bunch of traditions that people do to make themselves feel better, which means they have no love of the truth (i.e. the Word) that they might be saved.
And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved.
-2Th 2:10
They consider not that they do evil.
Keep thy foot when thou goest to the house of God, and be more ready to hear, than to give the sacrifice of fools: for they consider not that they do evil.
-Ecc 5:1