Well put together article from http://www.catholic.com/magazine/articles/does-the-watch-tower-society-speak-for-god
Contradictory Doctrines
The Jehovah’s Witnesses have a doctrine known as the "increase of light." It is based on Proverbs 4:18, which in their New World Translation of the Bible reads, "But the path of the righteous ones is like the bright light that is getting lighter and lighter until the day is firmly established." Witnesses understand this passage to mean that God reveals to them a progressively greater understanding of the Bible, known as "light." Over the course of time, then, the WTS is becoming more accurate in its interpretation of the Bible and in its prophecies, as the "light" shines more brightly.
While Catholics agree with the idea of doctrinal development, that is not the process actually taking place within the WTS. When a teaching or belief genuinely develops, its essence remains intact as expanded layers of understanding are added to it. In fact, the first president of the WTS, Charles Taze Russell, said: "A new light of truth can never contradict a former truth. ‘New light’ never extinguishes older ‘light,’ but adds to it" (WT, Feb. 1881, 3).
When we examine the history of the WTS teachings, though, we see a very different reality. Many WTS doctrines are contradictory or have been reversed, abandoned, or flip-flopped back and forth between interpretations. As Jehovah’s Witnesses became increasingly aware of this, the WTS had to account for it and so compared its doctrinal changes to a ship tacking in the wind (WT, Dec. 1, 1981, 27). A drawing accompanying the article shows a sailboat zig-zagging toward its destination. The reader is assured that the boat ultimately gets where it is headed. This explanation may satisfy some, but to others it is an attempt to cover up a history of doctrinal confusion.
Here are some examples of the WTS extinguishing one "light" for another:
The Great Pyramid of Giza is "God’s stone witness" detailing his plan for humanity (Studies in the Scriptures, vol. 3, 1890, 313) and later a "monument of demonism" (WT, Nov. 15, 1955, 697).
Jesus should be worshiped (WT, Jul. 15, 1898, 216); then he should receive only "relative worship" (WT, Jan. 15, 1992, 23); then relative worship is forbidden (Make Sure of All Things, 1965 edition, 249); finally, he should not be worshiped (WT, Nov. 1, 1964, 671).
The sower of the seed in the parable of the mustard seed (Matt. 13:31–32), is Satan (Man’s Salvation Out of World Distress Is at Hand, 1975, 208), and, in the same year, it is Jesus (WT, Oct. 1, 1975, 600).
The men of Sodom and Gomorrah are to be resurrected (The Harp of God, 1921, 344), then not resurrected (WT, Jun. 1, 1952, 338), then resurrected (WT, Aug. 1, 1965, 479), then not resurrected (WT, Jun. 1, 1988, 30–31).
The "higher authorities" of Romans 13:1 are earthly governments (Studies in the Scriptures, vol. 2, 1889, 81), then Jesus and Jehovah (WT, Jun. 1, 1929, 165), then the commercial and political elements of Satan’s organization (Preparation, 1933, 127), then Jehovah and Jesus (Salvation, 1939, 58), then human governments once again (WT, Nov. 15, 1962, 686).
The WTS has said: "It is a serious matter to present God and Christ in one way, then find that our understanding of the major teachings and fundamental doctrines of the scriptures were in error, and then after that, to go back to the very doctrines that, by years of study, we have thoroughly determined to be in error. Christians cannot be vacillating—wishy-washy—about such fundamental teachings" (WT, May 15, 1976, 298).
The article went on to ask, "What confidence can one put in the sincerity or judgment of such persons?" This is a point to ponder seriously when assessing the reliability of the Watch Tower Society as a spiritual guide.