dozy - "...In one of Franz's books, the GB allude to this in one meeting when discussing the ministry and one of the GB members bewailing 'What will the brothers do, then?' when discussing the lack of biblical basis for the preaching work..."
I remember that bit.
Of course, the real reason for the door-to-door ministry was its record-keeping aspect.
The WTS has never been interested in things like soup kitchens or clothing drives (too little chance of return on the investment, I suppose)...
...so they needed something else to justify their "charity" status, and the sweet, sweet tax-exemption that comes with it.
And so was born house-to-house records, a.k.a. a paper trail, (that could also be easily backed up by visual confirmation from millions of annoyed homeowners) just in case they were ever audited.
Note: I suspect that - like the pedo problem - the rest of the GB were able to keep Ray Franz out of the loop about this particular quirk of the Org's business model.