1 Corinthians 15:33 Do not be misled: “Bad company corrupts good character.”
No matter how good you think you are, if you continue to watch bad things, mix with bad people and listen to bad people, then you will start to become used to those bad things, allowing them into your life.
Before long you may well be doing the same things as them, those very things that may have turned you off in the beginning now become part of your life, part of your being.
God wants us to be separate from these characters so that we will not be corrupted – it is much easier to give in to them that to train them in what they should be doing!