Wouldn't that break the "the unconditional right to privacy" line in the Constitution?
As someone who moderates forums on both sides of the debate, I think outright banning either gender is just a moderation nightmare. It makes people very paranoid, it forces people to give up their privacy for the sake of verification, and all you have to do is accuse someone of being the other gender to force them through the verification process. I personally think it's a waste of time for content moderators to be trying to spot a "gender" out rather than just enforcing content policies.
The primary concerns with .com's multi-gendered approach is there's just two different cultures and people don't like it. I think both genders contribute the same amount of slop and the same amount of shit questions. Men don't like the women's humor and the women don't like the men's humor. I don't think it actually has anything to do with the "value" either gender provides, but rather than the value they provide is different. Men's tutorials are just simply different than the women's.
Most of the issues have to do with e-dating. But it's very easy to enforce, you just ban people who mention it or act gay (matching profile pictures, etc).
I think focusing on trying to be niche/gatekeeping by adding new rules that blocks certain types of users instead of simply making it not appealing to normies on a content level would be defeat the overall objective you're trying to achieve with the "no rules" sales pitch.
Some websites will have etiquette recommendations or community culture expectations posts. These technically are not rules, but it teaches users what kind of culture you're trying to aim for and you can remove users under the assumption they're not a fit culturally in the community, which you have established is how you want removals to work most of the time. It would make sense it should be up to the community to determine what fits culturally.
The concern about it happening "too often" is putting the cart before the horse. You would learn how to deal with issues once you actually face them. If it happens then you would address it then, not before.