These days, Witnesses are quick to point out that they are eight million people strong. We’ve seen it in several comments they’ve posted. The implication being that eight million people can’t be wrong. It’s the same argument Elvis fans have used for years.
But let’s put it in perspective. There are currently nearly seven and a half billion people in the world. That makes Jehovah’s Witnesses just about one in a thousand. Can one in a thousand people be wrong? Of course. Put it another way: In an auditorium filled with a thousand people, what are the odds that 999 of them are wrong and only one of them is right?
It’s possible, but hardly a positive convincing argument in favor of the minority opinion.
But it’s worse than that. Since Armageddon is “any day now” (and has been for a long time), and since the Watchtower holds that everyone will get a chance to have “the truth” explained to them before Jesus’ army murders them for their willful unbelief, it means that 999 of them have had the truth explained to them and have willfully rejected it in favor of living a lie, knowing full well the life-and-death consequences of that decision!
Truth can never be told so as to be understood, and not be believed.
— William Blake
I agree with Blake. When I understand the truth about something I automatically believe it. I really have no choice in the matter; “understanding something as true” and “believing something” are virtually synonymous. The fact that the vast majority of people don’t believe the Watchtower religion after understanding it means that they are not convinced that it is true: not that they have “rejected the truth in favor of the lie.”
Arguing that something is true just because a number of people believe it to be true is a logical fallacy. It even has a fancy Latin name: argumentum ad populum (“appeal to the people”) and is well explained in this article on Wikipedia.
But it’s even more foolish to play this particular numbers game when you are a minority group. If the number of people espousing a religion were an indicator of its truthfulness, then you’d be wiser to cast your lot with the Catholics who outnumber the Witnesses 175 to one.
Now, as soon as we point out these facts, a Witness will forget about what they just said [hoping we will too] and immediately change tactics and tell us about how narrow is the way, and how 
“many are called but few are chosen” and all the other arguments they can come up with to prove the opposite point: that the true religion will have few adherents. Blowing raspberries is an appropriate response to this.
Playing with other numbers
Numbers play a surprisingly large role in the Watchtower’s doctrine and history. But it’s all terribly boring. So I thought up this little rhyme to help keep it all straight and in Watchtower perspective:
One: “godly org” on planet Earth.
1914: their everLASTing DAYS begin.
1919: they show their “worth.”
1945: saving lives becomes a sin.
Two: the witnesses in Revelation.
Millions: living who will “never die.”
Myriads: former members whom they shun.
Countless: each deception and each lie.
3 1/2: their time in prison.
Six-thousand: years man’s been around
607: their tunnel-vision.
One-thousand: years that Satan’s bound.
For godly perfection the number seven
simply cannot be compared.
12 is organization, and for heaven:
A thousand times that number squared!
Eight-million: doing Watchtower’s will.
666: that bad boy of the night.
Seven-billion: non-believers God will kill.
Zero: total times that they’ve been right.