So the theory goes that since the first millennium started in the year 1 that the third should start in the year 2001.
Besides the obvious fact that the vast majority of 3 billion people are all leaving the building in one direction, it seems prudent to leave with the flow than against it, there are other reasons to wonder about the accuracy of such a theory.
First consider that the first century did not start in the year one. Actually the first century actually never started. It was backdated, and quite inaccurately to boot. Best guesses would indicate about 7 years wrong. So if the current calendar would like to start at the birth of Jesus, the third millennium started about 6 years ago.
But even allowing for the scientific and mathematical among us to win the theoretical battle, it is just plain impractical to suggest that anything can change the momentum. It would be about as easy as changing Christmas from Dec 25th by arguing that Jesus was born in the summer time. It really doesn't matter what day Jesus was actually born, it only matters what day the population as a whole celebrates it. That is Dec 25th for the vast majority, just as the millennium will be celebrated next new years regardless of any arguments to the contrary.
One can apologise by decree...but that does not stop the earth from revolving about the sun. The third millennium will NOT begin until 2000 years have been COMPLETED. That is a truism. If three billion people get it wrong, that does not change the fact. Otherwise you might as well set the speed of light by referendum, and let pi equal 3 (think how much easier the computations would be.) The year 2000 will be special as the first four digit one to start with two (and perhaps the first to confuse millions of computers) but it will NOT begin the 21st century. But that doesn't mean you can't have a party if you want...you could also have one for Beethoven's birthday, the start of sheep shearing, or the 72nd anniversary of the decision of Coolidge not to run. You don't need a trumped up phony start of a millennium.
The basic problem is that the Hitler "big lie" technique seems to have been perfected. He attempted to persuade his people through the tools of communication available. Nowadays it is possible to do such things, for example, to persuade a mighty nation that one man lying about sex matters while the lies told by the other 78 million American men don't matter [oh sorry: are you an American male who has never lied about sex?]. You can persuade a smaller nation and much of rest of the world that a woman is an adulterer whose tits must be seen and private messages must be heard - and immediately she dies that she was just a tad away from Jesus Christ and Mother Theresa. You can persuade billions of people that, while the first millennium was the thousand years from 1 to 1000, the second millennium is the nine hundred and ninety-nine years from 1001 to 1999.
And why is the big lie technique perfected? Because when people point out the errors in these things, the populace does not care. Why spit against the wind? Why tell billions of people they are wrong?
I'll tell you why: because I am not going to give up in the path of the juggernaut. If this world is ever going to see real civilisation, in place of the awful society that is developing, the first thing it needs to do is to control the media. You do what you like, but I am not accepting lying because a billion people believe it or because a billion people want their sexual titillation.