This is a bad idea. In particular in the war on terror.
There is a great reason why we should both import and export from dictatorships. It is the best advertising America can ever get. In short, people who buy American products are less likely to hate America. They are able to see another picture of America, not just the political one.
You see, even European leftists tend to like America. Yes, they may hate America as a political player in world politics, but "American" is still something positive to them. American movies, food, drinks, sitcoms... we all enjoy them. If a movie is from America or has American actors in it, it will instantly get more interest than if it's Swedish. Virtually every American sitcom is shown on Swedish TV (Friends, That '70s show, 90210... personally, I'll never forgive you for 90210).
The english language also has a high reputation in Sweden - you are expected to know english, and be able to speak it fluently. The more you can conceal your accent, the better. Inability to speak english is seen as primitive. American is a synonym for something that is cool and modern.
In other words, even in the midst of a leftist country, no-one really hates America. We may hate your politicians (and really, don't people in the US hate their politicians too?), but we know that your politicians don't show the full picture of your country. Therefore, we would never attack you, because when we attack you, we don't really hurt the politicians. We only hurt the American people - and we actually like the American people, even though we can't always understand why you vote the way you do. Even hardcore leftists like the leader of a communist youthgroup admitted he thought America was a great country and that he loved New York - something you would never hear an islamist say. Yes, he hated America's foreign policy, but he'd never hate America just because of that.
It is simply harder for islamists to convince young people that America is the Great Satan if the kids have been drinking coca-cola and other products stamped with "Made in the USA" all their lives. It's harder to hate America once you've seen That '70s show or Two and a half men (but for God's sake never show them 90210, then it's really your own fault if they hate you) - yes, you may still dislike America politically, but you won't hate Americans the way you otherwise would. Your view, so to speak, would be more nuanced.
Every time someone consumes an American product and thinks "This is great" America's reputation in the world is improved and you become a little bit safer. In order to commit a terror attack against America or American soldiers abroad, you need to absolutely hate America. Disliking it isn't enough. If everyone in this world was convinced that there was at least something positive about America, something good worth preserving, then there would never be any terrorist attacks, because terrorists act with blind rage. This is not to say that America has caused or deserved this blind rage (it hasn't), but it is none the less true.
Now, someone may say that a lot of terrorists have gone to university in the west (some have even gone to top universities like Harvard and Princeton). That's true of course, but that's mainly the terrorist leaders - not the guys doing the dirty work. These terrorist leaders have been brainwashed since they were kids, and by the time they get to Harvard, it's too late to influence them. Or maybe they are being influenced by the liberal professors at the Ivy League schools, who seem to hate America as well. Is there any way we may be able convince the likes of Bin Laden to send their kids to Mississippi State University instead?
American corporations may have a reputation for bad ethical practices, but there is one value they are very good at promoting: Individualism. And individualism, one of the most American values that there are, is the exact opposite to terrorism. People who think of what kind of shoes would fit best with the "image" they want to create of themselves, simply have less time over to think of what kind of bomb would fit into said shoes (remember the shoebomber?).
These countries are already so isolated, so what good could possibly more isolation do?
This goes in particular for Cuba. If it was not for the embargo, the regime would be gone in a week. Communist regimes need enemies to survive, they need something they can unite the people against to make them forget about their low living standard. They need an excuse; even communists in Europe claim that the reason why Cuba is poor isn't because of the communism, it's because of the embargo. The embargo gives the regime an excuse when citizens ask when the communist utopia will arrive; "gee, we'd really like to get that utopia, but as you know we can't trade with the US so until that changes, we're kind of stuck where we are". By lifting the embargo, the US would show that they are not Cuba's enemy, and that excuse would be gone. Because, communism cannot enrich a country, whether you have trade with America or not. Yes, some trade is allowed, but why not just let it be free? The only people who suffer are the regular Cubans, not the elites.
There is another good reason to trade with dictatorships: The more a country trades, the richer it will be. And the richer it is, the harder it is to keep a dictatorship together. China is significantly more democratic today than it was during communism, not just because they dropped the communistic economic system, but because as people get richer and get to see more of the rest of the world, they want the same things everyone else has. There is a huge Chinese middleclass asking themselves things like "Why don't we get free Internet when the Americans get it?". Now, an isolated Cuban who hasn't seen the outside of his island for his entire life would never even think of asking that question. Neither would a North Korean, or for all that matters an Iraqi during Saddam Hussein.
By trading, we can undermine dictatorships from within. So let's do it.