Well a big part of the idea behind safe spaces is that they provide a useful function even in inclusive venues. The basic principle is that majority culture can be exclusionary even without overt hostility towards minorities simply through weight of numbers and the inherent otherness that that foments. A delineated safe space provides (at least in theory) some measure of relief from that. A safe space, as originally defined, pretty much can't exist in a way that encompasses the entirety of a venue which contains a representative cross-section of the population at large, because the demographic make-up of that group is inherently othering.
By way of example, even at explicitly feminist conventions it's not unheard-of to have designated safe spaces for racial, sexual, or gender minorities, and by the standards of general society there'd be few venues more conducive to being broad-based safe spaces than overt feminist gatherings. In American feminist discourse, specifically, ideas of safe spaces came partially to prominence as a direct result of the difficulties that the American feminist movement as a whole has had over the years in dealing with issues of race.
