It's very rare to hear actual arguments about keeping Cuba on the state sponsor of terrorism list, but my member of Congress has done so. It focuses mostly on old cases of people from the 1970s who committed crimes in the U.S. and fled to Cuba (do we base foreign policy on that?) and also the FARC, which of course is currently negotiating a globally-supported peace deal with Colombia. The North Korea connection is the only part that could legitimately be cited to determine a current threat to the United States, but one example alone is insufficient, especially since North Korea is not on the list.
He concludes with this:
Mr. President, you didn't seem to get the basic training in your youth to understand bad guys and how to pick your friends. The problem is that our national security has floundered, and we face graver and more perilous threats because of your naïve understanding of human nature and your bad judgment.
The idea that Cuba is a graver and more perilous threat in 2015 is beyond laughable. It's a dictatorship, but that is obviously different from posing a threat to the United States given the dictatorships we support.
At any rate, it's useful to see the reasoning. Maybe he can also provide a good rationale for the success of the Cuba embargo, since its own supporters keep neglecting to do so.