Why is the argument of missile defense in the nation of Cuba a non-starter?

The argument of missile defense in the nation of Cuba is a non-starter because the USA will never willingly allow a nation that is so close to its territory, and is an ally of its arch enemy, Russia, to have such a defensive system installed, because it will also mean that Russia may use Cuba as its military base and threaten the USA territory at any moment, from close proximity, and also they will have a protection by any attack as a response.