I wonder if getting baptized itself is a "contract".
In a sense yes, however, it is a contractual agreement to subject oneself to the organization's "religious court" system (i.e. judicial committees).
Has anyone ever wondered why after so many years, the Society saw fit to change the baptismal questions to include the verbal acknowledgement of being baptized into the organization? The Society's reasons were not purely theological. There were legal ramifications involved.
Ray Franz revealed that shortly before the Society changed the baptismal questions (in 1985), there were U.S. Supreme Court decisions which concluded that a member of a religious organization can be made subject to its internal courts without due process afforded under the U.S. Constitution.
Some Jehovah's Witnesses it the past had responded to judicial committee summons by hiring an attorney to send the body of elders a letter instructing them to discontinue correspondence with the member and to deal exclusively with legal council. This created legal hassles for not only the local bodies of elders, but for the branches, and headquarters.
Under the new U.S. Supreme Court decisions however, a member could be subjected to religious tribunals without legal representation. Such decisions protected religious organizations that practice ex-communication from costly litigation.
So, the Society changed the wording of the baptismal questions in order to shield themselves (and the local congregations) from lawsuits by those who were disfellowshipped. Ray Franz in his book "In Search of Christian Freedom", revealed that the Society's legal department has crafted a lengthy legal package that is mailed to attorneys who might be hired by an indivdual Witness who challenges a judicial committee. The legal package makes references to the U.S. Supreme Court decisions, as well as the legally binding "contractual" relationship that the individual JW member entered into upon their baptism.
This is one case in which the Jehovah's Witnesses are now officially (and legally) a religion with a clergy and laity. It's interesting that this kind of arrangement was denounced by C.T. Russell and Judge Rutherford as one of the characteristics of Christendome. However, as has been the case with so many other issues in the Watchtower organization, cynical pragmaticism has won out over strict Biblical adherence.