If the JW baptism rite were strictly an agreement of sorts between the one baptized and God, there would be no problem. But the Society adds a great deal of legal baggage to the rite and makes it into a legally enforceable vow to obey the Society no matter what it instructs.
Until 1985 this enforcement came strictly through the practice of disfellowshipping, where a person who was baptized at any age and no matter how long ago could `legally' be DF'd via the Society's "judicial process". An example of this was when author and professor of religion Edmund Gruss was DF'd around 1971 for publishing a book critical of JWs. Gruss was baptized at about age 16 in the late 1940s and quit the JWs at age 18, and eventually became a member of some Evangelical style religion.
In 1985 the Society inserted some quasi-legal language into the baptismal vows, where the person explicitly agrees to obey Society representatives who are "in connection with Jehovah's spirit-directed organization". Now, in most countries a person under 18 cannot be held legally responsible for entering into a "legal" agreement. Thus, until the person is 18 that baptism is technically unenforceable if someone wanted to push the issue in the courts. However, if the person continues as a JW much past his or her 18th birthday, then he or she becomes a de facto JW by reason of publicly declaring, by their conduct, that they have as an adult validated their baptismal vow. Of course, the Society never informs anyone about these things, and JW parents rarely if ever tell their JW kids about them, and so it would take an unusually mature teenager to realize that the threat of DF'ing is probably legally unenforceable while they're under 18. And of course, how many teenagers that age have the balls or the resources to fight Dad, Mom, family, friends and the Society?
For these reasons I think that the Watchtower Society is morally repugnant for creating a social/religious atmosphere in which minors are forced or strongly influenced to make and continue obeying what ought to be adult agreements to obey the Society.