I don't think the Watchtower's copyright claim would survive if fair use was claimed:
From wikipedia:
Copyright does not prohibit all copying or replication. In the United States, the fair use doctrine, codified by the Copyright Act of 1976 as 17 U.S.C. Section 107, permits some copying and distribution without permission of the copyright holder or payment to same. The statute does not clearly define fair use, but instead gives four non-exclusive factors to consider in a fair use analysis. Those factors are:
- the purpose and character of your use
- the nature of the copyrighted work
- what amount and proportion of the whole work was taken, and
- the effect of the use upon the potential market for or value of the copyrighted work.
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Firstly, the primary purpose in reproducing the letter was to expose the dubious policies of the Watchtower corporation.
Secondly there was no monatary gain in reproducing the letter, the primary purpose was its news worthiness.
Thirdly, although the whole letter was reproduced it was to show that the information was not fabricated by apostates, but was legitimate.
Lastly, by reproducing the letter, no inherent monetary value of the letter was decreased.