Ostensibly, arguing the need for a male-oriented space implies that the default/mainstream spaces aren't already male-oriented. AFAIK, there isn't a huge outcry against male nurse associations: https://en.wikipedia.org/wiki/AAMN
Currently men make up approximately a third of victims but have approximately 0% of the shelters.
If you scroll through the comments here, you may find that it's not a foregone conclusion that the mainstream spaces are necessarily male-oriented. Quite a few people feel the opposite, in fact.