No one can prove 100% that nothing is going to happen on any day chosen at random. We have, however, proven that the doomsday scenarios claimed by the 2012 hoaxers either
1. can't happen at all
2. can't happen by 2012
3. are regular events that don't harm us
4. or the likelihood of happening in 2012 is no greater for 2012 than any other time.
As for Nostradamus and the Maya, they didn't come up with ANY date. Neither of them made any such prediction. Nostradamus never mentioned 2012, but his predictions go up to the year 4797. The Mayan calendar doesn't end, but starts a new cycle. The Maya mentioned 2012 only once, in a defaced inscription that says nothing about any cataclysm or the end of the world. They do, however, have an inscription about an anniversary celebration to take place in 4771.
By the way, if the world were ending, everyone would die whether they believed it it or not, so don't pretend that we would get anyone killed. There are no precautions that will protect one against the end of the world, other than a tinfoil hat.