That said, if I was in an all-woman clothing store (and for the sake of arguement, let's assume males are forbidden to even enter this hypothetical store), I would not be expecting women to be walking out of the cubicles in their underwear or half dressed. In fact, if they were, I'd walk straight out of the shop and never come back. That's way more intrusive for me than unisex change rooms. For me, it comes down to respecting boundaries. We each have our own boundaries and what we're comfortable with. I guess I'm trying to say - don't assume your boundaries are the same for all women. What bugs you - I'm fine with. And what you're fine with - bugs me.
And for the record, I actually buy nearly all of my bathing suits from sports warehouses (because they sell more practical swimwear that you can actually swim in and dive without bits coming adrift). Those places have unisex change rooms and tend to be male-dominated. It's never occurred to me to feel uncomfortable trying on swimwear there because I try that on in the cubicles with a locked door, just like I do in women's stores.