So let me get this straight. They are choosing not to train because part of the training is against their perceived religious convictions which prohibit interaction with other genders.
This really hits the nail on the head. Although the sensei may be saying "go away [insert X group here]" (though hopefully he isn't), it seems more like them choosing not to participate because they don't like a certain aspect of it. Which is fine. I think pottery would be great if it wasn't for all the damned mess. So I take it upon myself not to do it.
It puts you in mind of the kind of people who would sue a dairy farm because their allergies stop them drinking milk. No one is forcing you to do Aikido, so if you don't like what it involves then don't do it. Other activities such as work (which arguably is
a daily requirement for life) then sure, make allowances for reasonable religious customs. But a hobby? Why would you choose to go out of your way to do something which is blasphemous to your religion?
Although... when God gives you lemons, you get a new god!
The way you train is adjusted to your beliefs, they want to train according to their beliefs.
Then surely what they want isn't what's on offer?
Let us not forget that most sensei give up their free time to teach us Aikido for nothing other than the pleasure of doing so. Martial arts (especially Aikido) are very much rooted in Japanese culture. To learn Aikido is to accept that you're learning and practicing East-Asian customs. That is what the instructor has chosen to teach. If you don't like it then find someone who's willing to teach you whatever it is exactly that meets your requirements, or play ball long enough to be that person yourself. Sensei doesn't have
to keep coming every night; they could just as easily pack it in and teach no one, if their students think they know better about what constitutes Japanese customs. You simply cannot say that you want to learn something Japanese but not be okay with something as fundamentally Japanese as bowing.
My God, I wouldn't go into a Hindu temple upon my own volition and insist they let me read the Bible.