Ships - ships big enough to do material damage would be very small in # - ships big enough to do material damage would have a (somewhat?) professional crew - whatever damage they could do would always be limited to tiny areas - only where water & land meet, only where substantial public or private investment had been made in docks/etc - operators have strong financial incentive to avoid damaging ship or 3rd party property (public or private)
Cars - in some countries the ratio of cars to people is approaching 1 - a vanishingly small portion of vehicles have professional drivers - car operators expect to be able to operate at velocities fatal to others on nearly 100% of land in cities, excepting only land that already has a building on it, and sometimes not even that. - car operators rarely held liable for damage to public property, injury, or death and there's strong political pressure to socialize damage and avoid realistic risk premiums
I don't love flock but IMO the only realistic way to get rid of license plates would be mandatory speed governors that keep vehicles from going more than like 15mph. I would be fine with that, but I suspect most would not. If we expect to operate cars at velocities fatal to people outside our vehicles, then there will always be pressure to have a way of identifying bad actors who put others at risk.