What is the ruling on buying and selling empty cassette and video tapes in the four schools of thought, taking into consideration that the default status of things is permissibility?

It is true that the default ruling for things is permissibility (ibahah), and that means take the rulings of their ends (maqasid), and whatever leads to the forbidden is itself forbidden. Scholars have explicitly prohibited selling grapes to someone who will use them to make wine, because it is assisting in sin, in accordance with the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." It is narrated that Sa'd ibn Abi Waqqas ordered the uprooting of grapevines that were only suitable for making wine, and he said: "What a wretched old man I would be if I sold wine." Based on this, there is no harm in selling and buying blank cassette and video tapes, unless it is known or strongly suspected that they will be used for forbidden purposes.