"Adjusted explanation: Jesus was not foretelling that a group of his anointed followers would make up a wicked slave class. Rather, he was warning his followers about what would happen if they thought and acted in a way that would cause him to view them as wicked and sluggish."
Every time God gave the new nation of Israel a warning of consequences associated with breaking His laws, the Israelites ended up breaking those laws and reaping the consequences.
"If you do THIS, I will do THIS."
These were not shoot-from-the-hip warnings over abstract concepts of future possibilities. GOD KNEW what those punks were like and what they were GOING TO DO. So, he gave them a heads up.
There is no scriptural basis for the GB to make the assertion that a warning was given about something that would never happen. The record speaks volumes to the contrary.