Quite a lot of people, myself included, don't agree that what is "better for humanity" is the best option when it comes at a massive cost to other aspects of the natural world.
I'm now curious how one would estimate the number of megadeaths would result from the elimination of all oceangoing trade and ocean fishing. Heck, what percentage of only Japan's 127 million people would starve?
It really isn't. We need the oceans. Your proposed course of action has unimaginably large costs, no prospective benefit, and indefinite duration.