Christians who rely on the New Testament alone in drawing conclusions about the Sadducees and Pharisees end up with a warped picture. The reason is that the New Testament texts were not intended by their writers to be historical accounts or biographies of Jesus. The words of Christian gospel were a combination of catechesis and polemics, designed to educate, proselytize, and propagandize all at once.
The Gospels were composed in their present form after the Roman war and the destruction of the Second Temple. This event left all the Jewish religious movements in a predicament (including the early Christians who saw themselves as Jews also), and this was not so much because the Temple itself had fallen.
Under Roman law, the only religion besides the state’s paganism that was allowed in the empire was the worship of the Jews. All other forms of worship were outlawed. You either worshiped the Roman gods or because you were a Jew (or favored their religion) worshiped the God of Abraham. Worshipping a foreign deity from a different kingdom independent of Rome’s jurisdiction was tantamount to treason.
The Romans never intended to destroy the Temple during the wars. As Judaism was an approved religion practiced by many Roman citizens, the Temple of Jerusalem was a landmark of Roman civilization. The Temple fell due to a mistake carried out by the soldiers under Titus, a mistake Rome tried to undo when Emperor Julian, in 363 as part of his plan to revive Roman religion (which included Judaism) in his attempt to squash out Christianity, ordered it rebuilt. Though the order never came to fruition, the fact demonstrates the favored (and most especially legal) position Jewish worship held in ancient Rome.
You see when the Temple fell, a competition in the Jewish community arose. Vying for validity in the eyes of the empire, Christians competed with the Pharisees over who were the true and rightful Jews. It was during this period that the written Gospels, especially Matthew’s, took shape. The negative description of the Pharisees in the Gospels was glossed over in rhetoric as Christianity was striving for what it believed was its rightful place as a legal religion. Much like Watchtower publications draws pictures of crazy-eyed clergymen appearing pompous and radical, the written Gospels did similar things with the competing Jewish groups in an attempt to say: We are the one true Jewish religion.
Without the Temple, the priestly sects of the Essenes and the Sadducees disappeared. Since the Pharisees centered on obedience to and study of Torah, they survived. You read nothing about the Essenes in Christian writ, only a little about the Sadducees, but a lot about the Pharisees because of this. The battle for the right to be recognized the authentic "Jews" led to the Pharisees as described in the New Testament to be written as polemic caricatures. Early Jewish descriptions of Christians were likewise colored with negative rhetoric, meaning that the truth about both groups (Jews and Christians) is actually somewhere in between.
Eventually Christianity was legalized in Rome, becoming the state religion. The persecuted became the persecutors because as soon as they realized they no longer needed to fight for the recognition of the worship as Jewish, they began a systematic oppression of the Jews that led to pogroms, the Spanish Inquisition and expelling of the Jews in 1492 from Spain, and eventually laid the groundwork for the ideology of Adolf Hitler’s “solution” regarding the Jews. Today Christians are making formal apologies for these mistakes, even rewriting their theology and admitting that these descriptions in the New Testament are colored with anti-Semitism. Groups like the Roman Catholic Church, some Lutherans, and even a few Evangelicals are coming to grips with the fact that they were virtually the inventors of anti-Semitism that laid the groundwork for the ideologies that inspired the Holocaust, though some more conservative members among them still disagree with and/or debate this.
It would be incorrect to claim that the JWs were therefore like the Pharisees and Sadducees of the first century as described in the Gospels. In fact, the Witnesses are closer to the Gospel writers who gave us some not-so-accurate caricatures that have led to 2000 years of hate crimes.