The WT claiming that all their false claims and predictions were done "sincerely" does not cut it, every religion claims it is sincere, and the WT has pointed out that such sincerity is simply not enough if they "teach falsehood".
I do not agree with the above poster who claims that false predictions were not made in the first century, of course they were, hence the excuse in 2Peter 3, many verses speak as though the "End" is near.
And if Jesus really spoke the words that Matthew and Luke give him about the generation he lived and taught amongst seeing the 2nd Coming, he was a false prophet too !