Because we are told to.
“Do not judge according to appearance, but judge with righteous judgment.” John 7:24
The Greek word for judge is “krino” and it means “to call into question”. This is what Jesus means when He says “judge with righteous judgment”. We are to call into question the unbiblical actions of individuals and discern for ourselves whether or not to follow such a person.
I Corinthians 2:15 But he that is spiritual judgeth all things, yet he himself is judged of no man.
"Dare any of you, having a matter against another, go to law before the unjust, and not before the saints? Do ye not know that the saints shall judge the world? and if the world shall be judged by you, are ye unworthy to judge the smallest matters? Know ye not that we shall judge angels? how much more things that pertain to this life? If then ye have judgments of things pertaining to this life, set them to judge who are least esteemed in the church. I speak to your shame. Is it so, that there is not a wise man among you? no, not one that shall be able to judge between his brethren?" (I Cor. 6:1-5)
Bear, I agree we are called to judge at times - however - in this case, I was just commenting rather flippantly. That flippant observation is that if a Presbyterian Pastor underwent something this dramatic involving another denomination, church, etc, then something is askew with his faith at some point.
And wow, did it strike a nerve, which in and of itself is instructive.