Of course, the Cubans could have disclaimed the Platt Amendment and discarded it from their constitution after the Americans withdrew. However, its provisions were also codified in a Cuban-American Treaty signed in 1903, and thus they were barred from altering their relationship to the United States in perpetuity.
Although most of the provisions of the Platt Amendment were negotiated out of existence in 1934, as part of Franklin Roosevelt's Good Neighbor Policy, one remained in effect and has been an unrelenting irritant to Fidel Castro: the perpetual lease of Guantanamo Bay.
Often times, those who protest governmental policies and actions are more concerned with contemporary and changing senses of what is fair, but have little knowledge of law, especially international law. However, governments, as well as individuals and businesses, depend upon the sanctity of contracts.