Please cite the church fathers who actually set dates. I am aware that some expected the return of Christ possibly within their lifetime, but I'm not aware of any orthodox Christian writers in the early years who went so far as to set specific dates.
"Born again Christians" do not have a monolithic organization as the JWs do, so there is no mechanism by which false teachers are regulated other than the local church (or the hierarchial church in some denominations). If someone is a false prophet or teacher and is independent of any local or denominational church, then you can hardly expect to hold every Christian everywhere responsible for the false teachings. Many, many BACs, for example, were and are teaching against the false prophecy of Harold Camping. It hardly makes sense to try to pin them with responsibility for a teaching that they opposed. JWs are universally expected to accept and teach whatever doctrines the WTS advanced; that's a whole different matter. If they advocate what the orgnaization teaches, and the organization is provably wrong, then they can be held to be in error. Likewise, anyone who claims to be a BAC but supports the teaching of, for example, Harold Camping deserves the label of false teacher.
To try to equate the body of Christ with the JW organization is a category error. The body of Christ is a spiritual, invisible organism, not a visible, human organization. No human can be absolutely certain as to who is a member. The pious person who has been sitting in the pew next to you for 20 years might be a total hypocritem, and the person you would regard as marginal in the faith might be truly devoted. Jesus said the wheat and weeds would grow together until the end of the age, and only at that time would it become obvious which was which. Just claiming to be a Christian doesn't actually make you one in the biblical sense. Jesus said that false teachers and false prophets would arise and deceive many. The existence of the false does not negate the existence of the true, nor is it necessary to condemn the true because of the errors of the false.