Mining nodules from the ocean floor is fine in principle, but the details can destroy ecosystems.

If precautions made mining twice as expensive, it would still be profitable (if not now, then in 10 years) and could extract all the metal we need while avoiding the damage.

Speaking of ships and transponders, while it would be easy for a ship to switch off its transponder, this would be easily detectable. Unless the ship hid forever, it would be found later. With a suitable legal regime, captains would not dare do that.