All of these "threats" you mention have
nothing pertaining to Cuba. No matter if Russia has nukes pointed at us or not, they don't need Cuba to launch an attack. Also, China is communist and guilty of the same crimes as Cuba in regards to freedoms and rights, why not embargo them as well?
Its a good question with really only one answer.
We're too economically involved with China and a embargo of a nation that size isn't a practical solution to anything really.
Embargo's in themselves don't stop Nation States from misbehaving, nor from building Nukes or locking up disidents.
But too think we're safer today than we were in the 80s is a bit naive I think.
My oldest is in the Navy, 5 years and I like to try an needle as much information out of him as possible when he gets home.
So, with out getting in trouble he basically tells me that the threat of our Boomers ( Ballistic Missle Subs ) are essentially whats keeping large Nations that may decide to go rogue or attack disputed island territories ( Japan and Tawain ) halfway honest.
That although China is on a mission to steal as much tech from the American millitary as possible, they STILL lack the abillity to excel in tech on their own. ( for some reason )
The Communist State isolates itself on a technological basis by impeding on the creative process of free people and further isolates itself by limiting the free exchange of ideas from people that may want to move there.
Its why the Soviet Union routinely offered up junk in response to Americans technological advances from the 60s to the present.
We made the SR-71 Blackbird, they made the FoxBatt-50 that turned out to be a heap of heavy junk. We successfully landed men on the moon 6 times and 3 rovers while they stranded dogs in space.
Even Russian and North Korea know we could have boats parked unseen and undetected off their coast at any time with the capacity to rain down 250 warheads on their major ciy's within a 15 minute time frame, per boat.
Now if that information is common, imagine what we don't know.
Cuba is still run by Communist Dictators and Obama should have ignored what is essentaially a thug pretedning to celebrate " unity " and freedom.