Liza,
I have no idea what would or would not convince you. But I can share what convinced me. Studying the Watchtower Society's publications convinced me. Not just the ones they direct you to for answers, but also the ones they wish had never been published. There are instances of convincing proof in both current doctrine and past doctrine. Mountains of them.
To avoid overloading you, I will share three and let you decide whether you would like to ask for more:
--1--
According to the most current JW doctrine on the subject Jesus IS NOT the mediator for all mankind; rather he is the mediator for only the 144,000. See for yourself on 2005 Watchtower Library CD ROM: "Worldwide Security Under the 'Prince of Peace'" page 10 paragraph 15, 16.
Jesus IS my mediator. No amount of religious dogma will separate me from Him. Common sense tells me that anyone who TRIES to separate me from Jesus is no relative of His. Therefore, I am convinced.
--2--
Matthew 28:18-20 is used by Jehovah's Witnesses for two purposes: They see it as a commandment from Christ to each of his individual disciples that they must preach and they see the fact that they each individually preach as proof that they are Christ's disciples. The logic works like this: Jesus told every one of his disciples to preach, every one of Jehovah's Witnesses preach, therefore we are Jesus' disciples.
READ Matthew 28:18-20 to yourself carefully so you can answer one simple question. Do Jehovah's Witnesses also each individually baptize other people? Because ... if their understanding is correct that this is a mandate from Christ for every disciple of His then they MUST also baptize people in order to fulfill this commandment.
Then consider this: Learning ABOUT someone doesn't create a personal relationship with that person. I could learn all there is to know about Abraham Lincoln and never have a personal relationship with him, for instance. Christian baptism creates the bond between Christ and the individual and between the Father and the individual and between the Holy Ghost and the individual. Peter wrote that baptism saves people just as the ark saved Noah and his family. (1 Peter 3:20-22)
So, the most important part of the "mandate" in Matthew 28:18-20 is NOT carried out by every individual JW. In fact, this most important activity of the First Century Christian church which could be carried out immediately wherever there was a convenient body of water nearby, this sacrosanct rite of Christianity ... has to wait for a Convention or an Assembly among Jehovah's Witnesses.
I do not think Matthew 28:18-20 is a mandate because it is predicated on Jesus having received all authority. Keeping the context in mind it appears (personal opinion) that prior to this he did not have the personal authority to grant them to do this work. Here he is sending them as his representatives to the world and is reassuring them that his authority will back them in this effort.
But IF IT IS a mandate Jehovah's Witnesses flatly ignore the most important part of it, the part which opens a personal relationship with the Father and the Son. Therefore, I am convinced.
--3--
According to the most current JW doctrine the modern Faithful Slave (a.k.a. "the wise virgins" of parable; Matthew 25) were selected by Jesus in 1919 not because of their correct doctrines or their behavior being so much better than everyone else. They were selected because they alone were waiting for the presence of Jesus to begin in 1914 (in expectation of the bridegroom's arrival). However, Watchtower publications from the time demonstrate conclusively that (in 1919) they WERE NOT waiting for Christ to arrive in 1914. They were teaching that Christ's presence had begun in 1874, that the Great Tribulation had begun in 1878, and that Armageddon had begun in 1914. Thus the popular talk series by J.F. Rutherford from 1918-1922 "The World Has Ended—Millions Now Living Will Never Die" Look the talk title up on the CD ROM.
The WT publication, written by J.F. Rutherford, by the name "Millions Now Living Will Never Die" related emphatically that the ancient worthies such as Daniel and Moses would be resurrected to earth in 1925. In this book, the date 1925 was said to be fixed even more firmly by Bible Chronology than 1914.
The fruit false prophets bear is prophecies that don't come true. The Bible Students/Jehovah's Witnesses began as false prophets, a doomsday cult. False prophets do not become true prophets. (Deuteronomy 18:20-22; 1 John 4:1; Matthew 7:15-20) Therefore, I am convinced.
As I said, only three. If you want more, just ask. There are dozens.
Respectfully,
AuldSoul