Any risks to sovereignty from ratifying UNCLOS are negligible compared to potential gains for national security
Protecting national sovereignty is a legitimate aim -- and one that some liberal internationalists may have been too cavalier about in the past. But for the goal to have any meaning, it must be framed so that it can be met. This is certainly what Reagan had in mind when he articulated a specific set of problems with the original UNCLOS that could be (and eventually were) dealt with. This time around, however, those who object to the treaty have defined sovereignty in such ideological terms that they will never be satisfied. By their reckoning, the United States can never be party to an international organization, even if it has veto status in it.
An international organization might very marginally limit U.S. freedom of action, but this is negligible in comparison to the harm that instability and conflict in the South China Sea could inflict on U.S. interests. Previous presidents from both parties understood the trade-off: In challenging times, and to exercise global leadership, Washington protected its interests by making enlightened commitments overseas, whether in the form of alliances, institutions, or foreign assistance.
The sovereignty costs associated with the Convention are grossly overstated primarily because many of these costs have already been accepted by the United States. In addition, the U.S. stands to gain sovereignty over 4.1 million square miles of territory by acceeding to the treaty.