Your friend can believe as he likes and do as he likes (within reason for there are consequences), because the Lord gave us free will.
The question is should he?
He can go around bullying, but then he will be a bully, abusing power.
He can go around sinning, but then he will be a sinner. He can take it further and be an unrepentant sinner, but then he will be Damned.
He can choose not to have self control and lash out at people close to him, but then he will be can out of control abuser.
Your friend can choose to believe what he likes.
He can judge a person by the cover, beauty, race, gender, but then he will only see only what is shallow, superficial and superfluous.
He can hate those that do not contort to his idea of perfection, but then he will be a hater, in the box limiter or a person never knowing growth with the Holy Spirit.
You can do and believe many things.
The question is should you do anything you want and believe anything you want without regard to the Lord's Commandments and consideration for those around you?