Men who take issue with women-only gyms are just self-reporting. Women aren't going to these places to practice witchcraft and plan world domination (usually). They just want to workout in peace.

And until there is a significant change in men's gym culture, women-only gyms are a natural solution.

Any reasonable man isn't threatened by this. He understands that there is an ongoing issue that hasn't been remedied. He goes to the gym to workout, and doesn't feel entitled to sexualize women as they exercise.

Simple as.