You have not given any reason 'not' to use fish either. Many of the products (if not all) state that you can add fish immediately. I don't understand the 'outrage' with using products as directed on their labels.
I appreciate your anecdotal evidence - I wonder then why so many others require 3 weeks, 6 weeks, even 6 months?
The thing is - its all about bacteria. Bacteria will multiply with fish waste, added ammonia, or time (as
@brandon429 has stated) - as things fall into the tank. To me there is no immorality using a fish to cycle. Note - this assumes that you have some product, old sand, an old filter, etc - providing enough bacteria such that ammonia levels do not get to toxic or even elevated levels.
Is the misunderstanding that you take a 100 gallon tank put a fish in and then they are subjected to 2 ppm ammonia and die in order to cycle the tank? That is not 'fish cycling'. Thats cruelty. To me using fish in 'starting a new aquarium' has no risk t the fish - and to me no reason not to do it.