The bottom of the ocean is a very large place and prime nodule territory required by humans is likely to be much less than one percent of that area. Sea bottom mining would exist only until asteroid collection becomes feasible. Say about 30 years. The alternative is severely degrading much of the above ocean environment. The modern world economy is filled with trade offs and this looks to be one of them.
Asteroid mining can’t come soon enough. We need an alternative to destroying this planet to satisfy our need rare earths.
Destroying our planet is cheaper. Money is all that counts.