I know that the basics of aikido can be taught and learned without mentioning the religion of O-Sensei, just as the basics of physics can be taught and learned without discussing Newton's experiments with cylinders. Solving simple problems in each area can be accomplished without deeper understanding. Still, I wouldn't consider either of these a complete education on either subject without touching on how these influences effected the development of each body of knowledge. The question was whether religion should play a part
in an aikido curriculum. To this I have to say that at the advanced level this must be yes. There is a difference between studying and practicing a religion; knowledge of physics does not a physicist make (mores the pity).
A separate question could be if the belief in or practice of
a particular religion should be compulsory
to the practice or curriculum of aikido. To that I would say no. Should a religious outlook
(set of ethical conduct) be a part of aikido curriculum? I think every responsible sensei should do that. There is a difference between teaching respect for oneself and others and attempts at conversion to the religion of The Founder (or others).
This is a classic hot button topic with many people, I can see that in the answers of many people to this question. Like so many times in society, the argument isn't really even about the original question, but about a related but different question. I bet that the majority of those that voted against the first proposition did so out of fear of the implications of the second that I mentioned. Many people read "play a part" and heard in their mind "have a major/dominating role" or "be the central soapbox issue for sensei in the dojo" reflexively instead.
Next time sensei can change my entire world view with a simple word and a gentle brush of ki (without the use of hallucinogens of course) I will remember to say, "Please sensei, may I have another!"
Note that the above statement doesn't imply that I or any sensei I know has ever used hallucinogenic substances to my knowledge or any reasonable suspicion on my part.
Note that the above explanation of the preceding statement was not meant to imply that I am a sensei myself (except perhaps in the area of physics and in whatever other areas that others are willing to endure).