This really strikes at the heart of the issue of national sovereignty .The US government wanted the revolutionary government out of power, and of course so did the corporations operating in Cuba. They wanted to deny the Cuban people their right to self-determination. And you're right, the refineries refused to work with Soviet oil, after the US decided to stop sending US oil to Cuba. Essentially, you had these private corporations and a foreign government trying to dictate Cuba's foreign policy to it! That they couldn't have normal and full normal relations with the Soviet Union.

That's the legacy of the blockade. The United States is dictating Cuba and other countries relate to each other. That's none of the US's business. And none of this is happening in a way that benefits the people of the United States. Whatever the initial justification of the blockade, Cuba has more than paid that price. The world recognizes that it must end, and it's been saying that for 30 years.