2000 was the last year of its decade not the 1st of this 1. The last year of this decade is 2010. The decade being discussed is 2001 - 2010.
This battle was fought a long time ago and the decision has been made by popular consensus. The 21st century started on January 1, 2000. Nobody wrote a song titled, "Tonight We're Gonna Party Like It's Two Thousand." December 31, 1999 was New Century's Eve.
I understand that there was no "Year Zero," but that's only important to a historian who has to calculate the number of days between May 1, 462 BCE and July 15, 639 CE. Besides, if you're looking for arithmetic consistency, how can you possibly tolerate the fact that, in the domain of calendars, -1 is followed directly by +1, with no 0 in between??? This is clearly not a nomenclature designed to please mathematicians so we just have to shut up and leave it alone.
Furthermore, every decade that has a name is named after its tens digit: the Gay Nineties, the Roaring Twenties, the Thirties, the Fifties, the Sixties. People talk casually about the Seventies, and they do NOT mean 1971-1980! The first decade of the new millennium will surely be named after the zero in its tens digit. The Washington Post, one of America's most influential newspapers, routinely calls it "the Aughts."
I'm happy enough that we no longer have to say "two thousand." Everybody said "two thousand nine," but they seem to have made the transition, finally, to "twenty ten."
There is no English Academy or Her Majesty's Office of Proper English. Unlike French and German, English is a democratic language whose vocabulary is defined by a consensus of its speakers. The consensus of its speakers is that a decade runs from the years 0 through 9.
Furthermore, if you'll feel better with a precedent, look at the way we tell time. Midnight tonight is 12:00 am Thursday, not 12:00pm Wednesday. The obvious reason is that we seem to believe that the first minute after 12:00pm Wednesday should logically be 12:01pm Wednesday, not 12:01am Thursday. By this same reasoning, 2000 and 2001 must be in the same millennium, and therefore the same decade. The fact that we call it "the twenty-first century" apparently doesn't bother us, and even if it did, pushing one year out of a hundred into the appropriately named century isn't going to make us any happier.
Obviously, you don't understand language, math or logic. So you blindly stubbornly persist in absurdity.
I'm done with your proud arrogant willful ignorance.
What all that adds up to is you can't add.
* * * * NOTE FROM THE MODERATOR * * * *
Personal insults are a violation of the rules of SciForums. For three in a row against the same member I'm supposed to ban you for one day. I'm going to let it go because I'm in a good mood and besides, I've never banned anybody on the Linguistics board. I never expected it to come up.
But if you do it again, I will have no choice. Dial it back please! If someone disagrees with you that doesn't mean there's anything wrong with him. Reasonable people disagree every day.