Founder-related Legitimacy Digs: telling somebody who practices aikido -- especially if you do not practice it yourself -- that they do not do what their founder intended is simply impolite and mostly pointless, even when presented in the most rational and polite way. Do not do it. I mean, you would probably not go on some religious forum and tell people their prophet was really not what they thought. Though there is historical evidence in that direction for many prophets. Slightly different field, same sensibility.
I like your post overall, but I must say I totally disagree with this. This is O-Sensei we're talking about. How are we possibly NOT to argue about what he was doing, how he was doing it, and how to reproduce it ourselves? And if part of the argument is that the core of what he was doing has been largely lost, how can that argument be made at all without saying "Most of you missed it"? Particularly when the argument has been made over the years with extensive research into the founder's actual circumstances, language, videos, training, and the reactions others had to his budo.
It's telling that you have to go to religion for your parallel. If you're seeing Aikido as a religion, you've got a problem. Other areas of human experience are
supposed to be debatable.
Arguing in the alternative, have you ever hung out on religion boards? Speaking as a follower of one of those prophets, let me tell you that telling each other that the other hasn't understood the prophet at all is a major source of entertainment and refreshment for all.