I didn't mean to imply that men's only gyms don't exist - they are a rarity though and most of those that do exist are the sort of place I wouldn't even consider joining for reasons that I probably don't need to enumerate here[1]. I should also add that I'm a little uncomfortable (what I said previously notwithstanding) with the fact that single-gender gyms exist from the standpoint of gym-as-business (as opposed to gym-as-place) and gender discrimination. It is, in general, in the US, considered counter to public policy for a business to have discriminatory practices in who it allows to be its customers. Gyms can get away with this (actually, I am unsure whether it has ever been adjudicated - but one would think so) because they are generally "private clubs" and as such mostly have the law on their side in terms of discriminatory practices (in choosing who can and cannot be members, though not, in most jurisdictions, with respect to hiring). That still bothers me a bit, as most gyms (of the sort that people like you and I use) are really more (for-profit) businesses than they are clubs as such. If e.g.- BJ's or Costco decided to have discriminatory membership practices, it would appear to be the case that, legally, they could. I know I would be bullshit about it if they did, though.

[1] Ok, I will, a little. It is my perception that such gyms are usually "old boys' clubs" and I find that sort of thing distasteful.