I'm not quite sure why people think the "wild west" is what is going to come of the various house militaries not being able to patrol in the border worlds anymore. The only reason the wild west was so wild is because of the presence of lawful government agencies trying to combat the outlaws, not outlaws running around with no opposition, which is what seems to be the ideal people want.
If they want house militaries to be more balanced in the border worlds, then restrict the types of ships they can use. I'd suggest letting them attack organisations in border worlds within their ZoI, but limiting them to no ships larger than cruisers, which makes a lot of sense from an inRP point of view, they're meant to be patrol craft to keep large unlawful groups in check.