I'm talking Realpolitik here, of course. But in the 70 years prior to 1945, no one dominated the oceans like America does today. Thus Japan, the US, Britain, France, and Holland all competed for dominance of the far eastern seas. Britain dominated the Indian Ocean, but had a few lesser rivals over the Atlantic, and the US controlled everything east of Hawaii.
The OP is arguing for a wider US withdrawal from our present domination of all three oceans. But what would happen in case of a power vacuum like that? I suspect in the far Pacific, you'd quickly see another competition between China and Japan, with South Korea freaking out and Indonesia slowly becoming a regional player. Taiwan would be peacefully reabsorbed and the people there would pray they get the Hong Kong treatment. Probably the Indonesians would seek help from Russia a/o India, neither of which would want either Asian giant winning this competition.
Competition for alpha male status among nations can turn ugly. But moreover, neither giant has the tradition that the United States has for supporting Freedom of the Seas. This term sounds like FDR to us, but it actually originates in Wilson's 14 Points, which in turn builds on the old Open Door Policy of the 19th century. Americans have traditionally pushed for open trade on the seas. Last time Japan was a player, they had a less liberal philosophy. China, psychologically still recovering from European & Japanese domination, would also be less liberal about sharing the seas.
If these two competed, because America withdrew, the chances of wars among their proxies and allies would increase exponentially. Under America's 70 year umbrella, there's been peace--the only exceptions have been peripheral and contained exceptions. Outside that umbrella, where there isn't dominance by major powers, the usual human atrocities prevail--Cambodia, East Timor, the periodic border skirmishes between China and Vietnam. But where the umbrella has extended, the major powers do not fight wars any longer. Compare the numbers of major wars between the 1870s and 1940s with the major wars since 1945. For that matter, compare the threats of war, the instances of successful saber-rattling between powers in those two time periods. By any measure, the Industrial Age was far more violent and far more dangerous than the Atomic Age and Post Cold War period.
For the Pacific Rim, at least, American naval dominance has been a boon. This is not to dismiss the problems that come with this role as global cop. American sailors have, on occasion, done terrible things to individual Okinawans. But in the big picture, in the strategic interests of the nation-states of the region, that doesn't matter too much. If you have a competition among nation-states for dominance of the region, individual human rights will come to matter even less.
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