A true child of God will accept only what God has said. If someone speaks or acts contrary to God's Word, then it is wrong.
We are told by God to judge....not the persons soul, but the actions. We can look at what someone is doing, and we can judge if it is right or wrong based on God's Word. We can not judge the persons motives or their heart, but we can say with authority that it is wrong or right.
And by the way, we are pretty quick to point the finger at ourselves also. Because, as the Bible says, "judgment begins at the house of the Lord".