I believe that Christ was speaking of them who were ignorant of His truth and His Gospel message. They were simply following the orders given to them by other ignorant individuals. They erroneously thought they were doing the right thing but were sadly mistaken.
Millions of lost souls today "know not what they do" and are simply following the "popular" opinions of the folks they surround themselves with. We can tacitly forgive them while praying that their eyes are opened to God's truth, His promises, His gifts, and His Kingdom.