Exactly! The US (or the land of freedom), doesn't let you in if they find out you've as much as visited Cuba. That's why Cuba gives you your visa in hand (as opposed to stuck in a page in your passport), so that you can still go to the US if you want to.

That is, unless you're Cuban. In that case you can go to the US and they'll welcome you to Miami with a red carpet and fool you with what freedom and cars and big houses and laptops you'll be able to have.