U.S. adversaries are using U.S. absence from UNCLOS to shape treaty in way adverse to U.S. interests
Similarly, less friendly countries such as China, Iran, and North Korea have sought to impose control over the ocean out to 200 miles off their coastlines by establishing security zones. Both types of proposed coastal-state regulations place at risk U.S. economic prosperity and national security by attempting to close off to U.S. ships and aircraft vast swaths of ocean, allowing coastal states at their whim to deny use of the global commons. These proposed restrictions by coastal states attempt to diminish or impair the right of freedom of navigation enjoyed by mariners for two millennia.
All of the countries mentioned above already belong to or have signed the convention, but are trying to change it through reinterpreting its terms. China, for example, is a party to the Law of the Sea, but denies that foreign warships have the right to enjoy high-seas freedom and overflight in the East China Sea. Beijing is patiently but steadily pushing to change standard interpretations of international law. By declining to become a member of the treaty, the United States has so far ceded the opportunity to influence and shape international norms, thereby yielding to states trying to popularize their restrictive approach to navigational rights.
South Carolina Sen. Jim DeMint, when leading the opposition to the treaty as it was being debated in 2007, said We know from international groups like the U.N. that many signers of these agreements do not act in the best interest of the United States or the world. He is correct, of course, but the United States' failure to ratify only empowers these states to set maritime rules without a U.S. seat at the table. DeMint's argument is akin to refusing to engage in debate on the future direction of the U.S. Constitution because one's political opponents have already staked out objectionable positions.
As the pre-eminent global maritime power, the U.S. has significant interests in the global effect of the Convention’s rules and their interpretation with many issues that of greater concern to us than to most other countries (for example, preserving freedom of navigation rights). Our adversaries view this as a weakness they can exploit and are shaping the course of the convention in ways adverse to U.S. interests while the U.S. remains on the sidelines, unable to participate in the discussion as a non-party.