I'm sure we were highly sensitive to everything that was going on in Cuba in those days. If our response to Castro's rise in Cuba seems like an "overreaction" now, it's because communism doesn't seem like much of a threat anymore. Perhaps now that worry seems a little paranoid, but the international political context was much different then.
However, I’m sure that we would be very concerned even today if we found that Russia, or any other country, was arming a close neighbor with an unfriendly government. In that respect, our reaction to the Cuban Missile Crisis wasn’t just a result of our fear of Castro.
It was also a test of wills between the U.S. and Russia. Russia was using Cuba to see how we would react to such a move. We would call it a “provocation.” Russia probably would have called it something else, like “helping an ally defend itself.” In Russia’s mind we did the same thing with our NATO allies in Europe. So, again, I think in a similar situation today we would have a similar reaction.