So if you had a vision you believe might be from God that told you to mow down a bunch of children with a machine gun or to do something you believed to be wrong or sinful, you would just do it?
See, I believe I can know God is good. His righteous and good ways are not a mystery to me. I am not in a Mystery religion. I am in a relationship with Jesus Christ and He can teach me His good ways. I can know them. For the Spirit guides me into all truth. God is not the author of confusion. He is not going to tell me to do good and then turn around and tell me to do something bad.
For Abraham did not believe he was going to just permanently murder his son. Hebrews 11:19 tells us Abraham believed God was going to resurrect Isaac. If Abraham did not believe God was going to resurrect Isaac, and that God was asking him to permanently take the life of his son, then I would believe this to be wrong because God does not ask us to break His own eternal moral Laws. God is good and His standard for righteousness is always good and knowable.