Look, everyone can see that your general argument makes some sense. Dividing people is bad, that is of course true. If male dominance in the dojo creates a barrier that keeps women out of the dojo, then by your own argument, something should change. So what can change? Well, someone creating an all-women dojo is one way. I think we all see the problem with that system of permanent divisiveness. No wonder the aforementioned dojo failed. This women's intro class however is a form of outreach, which by its very nature is a form of inclusion, not exclusion. I see it that way anyway. It is just 10 weeks of a class where women are not made to feel uncomfortable. There are still infinite weeks of classes where men are not made to feel uncomfortable, even on the same days as the women's class. It is hardly a case of male exclusion.
Myself, I wouldn't say that the answer to divisiveness is to create more divisions. At least, not unless the circumstances were fairly extreme.
"We're not anti-(xxx) we're pro-(xxx)" - insert your own groups, this is a pretty common argument. The problem is not that there are no alternatives for males or whatever group is excluded, the problem is the division itself. Wasn't that the question addressed in "Brown v. Board of Education"?