Here's a line of reasoning I will start using:
Where does the Governing Body get their information? The answer will be Jehovah's holy spirit.
If I told you that one thing you believed is no longer the case, wouldn't at least one of the two ideas have to be wrong? Of course, at least one would be incorrect.
Has God ever been wrong about anything?
Then their information couldn't possibly be coming from Jehovah. So if it's not coming from Jehovah, where is it coming from? It's coming from men. Does the Bible say we should put our trust in men? No
If they come back with, "but the Bible writers were men." Yes, but how many times did they change what they wrote? Zero.