I'm going to tell my friend he is being unfair to his kid
Why do you think they're being unfair?
I just want to help him be a better father and I cannot allow him to risk damaging his kid because of his selfishness.
Rather than trying to directly involve yourself in someone's parenting, set an example by your parenting. Show them how to do it right rather than telling them.
I will share my parenting experiences with my friend in hopes that he will realize that I am right.
That sounds like a really good idea. But, if you are concerned that your friend is actually causing real damage to his child, you should invite their kid to come hang out with your child, so you can show the child what a good parent acts like, and so they have some positive adult role models.