I have just become aware of a book, published in the US in 1935, called 'War is a Racket', by Smedley D Butler, a former Marine Major General who was very critical of the US involvement in WW1. Since it was apparently a popular book at the time, and Butler was a prominent figure, I am wondering if Rutherford's adoption of the slogan 'Religion is a Snare and a Racket' may have been borrowed from Butler.
If so, it wouldn't be the first time Rutherford drew upon familiar terms of the 20's and 30's to create slogans or WT articles.