The Watchtower Bible and Tract Society argues it is the True Religion on the basis of six biblical requirements that only they allegedly meet. Atheists may debate these biblical proofs with Jehovah's Witnesses at the front door or because they know Jehovah's Witnesses who wish to leave but are afraid because of nagging doubts. If atheists can refute the Watchtower Society's claim of meeting these Bible proofs, then the doubtful Witness may find it easier to leave with a clean conscience.
To be convincing, the Society's biblical proofs must be very specific and leave no room for doubt. They must point to the Watchtower Society and only the Watchtower Society — all other religions must be excluded. Only then can the Society claim to have proven they are the True Religion in accordance with the Bible rather than simply one of many equally plausible options.
Note: all of the following points are listed in chapter 15 ("Worship That God Approves") of the book called "What Does The Bible Really Teach?" as published in 2005 by the Watchtower Bible and Tract Society.
1. God’s servants base their teachings on the Bible (2 Timothy 3:16-17, 1 Thessalonians 2:13)
To most Christians, this is probably a given. Yet all Christians use the Bible, and there are more than 1,500 denominations in the United States alone. How can this requirement narrow our choices in a useful way? It seems likely that we should favor a religion whose teachings most accurately reflect those found in the Bible, yet no one can seem to agree on how to interpret it. If accuracy is the key, we might narrow our choices to religions whose teachings have gone relatively unchanged over the years. After all, every major change of doctrine suggests that the previous interpretation was wrong and that the organization has been adhering to an incorrect interpretation before the change was made. Since the Society is notorious for frequent changes in doctrine, this would actually seem to cast doubt on their candidacy as the only True Religion.
Whether they agree with this last point or not, this requirement is simply too vague to be of any real use.
2. Those who practice the true religion worship only Jehovah and make his name known (Matthew 4:10, John 17:6)
At first glance, one might think that the Society is an obvious favorite for this one. Jehovah's Witnesses not only preach the word of God from door to door, but they also have his name right there in the title. Except that "Jehovah" is not God's name. God's name is Yahweh. It might be better if they called themselves "Yahweh's Witnesses," but that just isn't the case. Besides, Witnesses are not the only Christians who preach door to door.
3. God’s people show genuine, unselfish love for one another (John 13:35)
There are many ways that this "genuine, unselfish love" can be shown. One of the Watchtower's favorite examples is their refusal to fight in the armed forces. They claim that any Christian risks killing other Christians in military engagements. (See chapter 15 from "What Does The Bible Really Teach?") Yet Jehovah's Witnesses are not the only Christians who refuse to fight in wars between nations, and this is not the only way that love can be shown. Charities and disaster relief efforts are examples of Christian love. Many would also argue that the practice of disfellowshipping (shunning and excommunicating) members is needlessly harsh. Disfellowshipping breaks up families and can prove dangerous to Witnesses who already suffer from clinical depression. There is little doubt that the Society isn't the worst at fulfilling this requirement, but surely it isn't the best either.
4. True Christians accept Jesus Christ as God’s means of salvation (Acts 4:12)
I'm unaware of any Christian denomination that doesn't meet this requirement. This is too vague.
5. True worshipers are no part of the world (John 18:36)
What does this biblical proof entail? Christians can't go live in outer space. The Society believes that being "no part of the world" means that Jehovah's Witnesses should avoid political entanglements or seeking "worldly pleasures" and virtues. But that's just one interpretation, one that many other denominations advocate. Some feel that putting Bible principles above "worldly" ones is enough, in which case most denominations could more or less qualify. Others, like the Anabaptist faiths, go even further than the Watchtower Society by isolating themselves into small communities. No matter how you interpret this one, it doesn't clearly single out Jehovah's Witness above any other group.
6. Jesus’ true followers preach that God’s Kingdom is mankind’s only hope (Matthew 24:14)
The Society claims that their door-to-door ministry is a fulfillment of this requirement. But they are not alone in the preaching work. Mormons, Christadelphians, and Seventh Day Adventists are among those who engage in similar efforts. In addition, the Catholic Church and many other Protestant denominations were making converts throughout the world centuries before the Watchtower Society ever appeared on the scene. If we consider how many generations of people became Christians due to these missionaries, the Society's Witnessing work simply pales in comparison. Even this requirement fails to single them out in any definitive way.
In the end, we find that none of the alleged biblical "proofs" point specifically to Jehovah's Witnesses, solely to Jehovah's Witnesses, or even to them at all. Another Witness favorite, the biblical claim that God's people will be hated by the world, doesn't help their case either. Many Christian denominations have been hated, both now and in the past. Quite a few mainstream Protestants claim to be persecuted even today, as do many Catholics. One could argue that Mormons and Anabaptists have been treated far worse than Jehovah's Witnesses.
Ultimately, then, the Watchtower Society's proofs don't prove anything definitively.