Six things...the last two are my favorite:
1. The WTBTS has logically incompatible beliefs. For example, evolution did not occur, yet we have organisms that are vastly different than their original form and function. They teach MORE evolution than any biologist ever would. For an herbivore to become a carnivore would take millions upon millions of years. That makes them guilty of teaching not ONE but TWO forms of logically incompatible nonsense. Further, they once taught theistic evolution (Photo Drama of Creation), stopped doing so for no specific reason, started pirating the lies of other fundamentalists and went on to accuse moderate accomodationists who say evolution is compatible with the bible as being immoral and sinful.
2. The WTBTS teaches the orthodox belief of Progressive Revelation which they disengenuously call "new light." The belief in spirit directed authority combined with progressive revelation produces a system of belief which, when viewed from the outside, could not possibly be falsified.
3. The WTBTS has never officially retracted any harmful teaching, never a single apology. A basic expectation of dignified, respectable, trustworthy individuals is that they admit when they are wrong. Even the Catholic church, which I equally detest for its historical atrocities has had the dignity, from time to time, to respond to well informed criticism in a grudgingly civilized way.
4. Not a single point of moral achievement or good is the unique province of a Jehovah's Witness. Not one. Yet there are many uniquely bad and harmful things within the religion.
5. Under no circumstances can a thinking person believe that an all loving, all wise, all powerful being could wait through 1800 years of human suffering, death and pain to finally in the late 1800's reach his hand into the mix and guide malcontented men through a century of endless equivocation, speculation and confusion to conclude that the grand creator of our cosmos is deeply concerned with your masturbatory habits, sexual positions with your wife and your choices in popular music. Furthermore, that he expects you to be totally credulous to the immoral preachments of his arrogant, ignorant, dotteringly elderly, secretive and capricious white american leaders.
6. That we should teach our children to hunger with great expectation for the slaughter of billions of humans who have no access to "The Truth" and have been given every conceivable evidence a rational person could want that the very message they are being executed for rejecting is the complete fabrication and wicked wishful thinking of anonymous octagenarians who have pick-pocketed the gullible masses in totalitarian, Orwellian deception since the preposterous shameful infancy of the faith.
Wicked, wicked fairy tales from poorly evolved mamals.