If that were only true, I think many would welcome the end of the world on Friday December 21. The real question is how would the Mayan's know this?
On November 8, 1519, the Aztec leader Montezuma met Cortés on the causeway leading into Tenochtitlan and the two leaders exchanged gifts. Montezuma gave Cortés the gift of an Aztec calendar, one disc of crafted gold and another of silver. (Wikipedia)
Clearly, the Aztec Calendar, which was derived from the Mayan Calendar, was partly responsible for Montezuma's defeat because of the superstitions associated with it. At that time the Mayan Empire was merely a shadow of their once great empire. None of this decline was predicted from their calendar.
Christianity had its own prediction of the end of the world in 64 CE (AD) and Nero used it to his advantage after the great fire in Rome to kill Peter and Paul and ruthlessly kill and torture Christians. See my book: 'The Seven Sisters and the Apocalypse'.
Calendar predictions are dangerous because they prey on the masses, who want things to be better and yet they do not accept that they could get worse! The annoying characteristic of change is that it can possibly take lifetimes to manifest. Who wants to wait for the joining of all races into a global truly democratic peace?
Thus when the aliens land and offer us their help on Friday December 21, many will accept them with open arms. Yet, they may really have intentions to destroy us all. Our defeat will be due to the Mayan Calendar or as people are saying an Obama Apocalypse.