> We already have a nontrivial number of women only events in technology.

To be fair, those make me uncomfortable as well. But there's a difference between "we're holding an exclusive event for group X only" and "group Y is banned because they have to be protected from group X who we want to be our only audience". There is also the power gap to consider, whether it is real or perceived doesn't matter. Holding an event for the perceived "underdog" is a lot less reprehensible than accommodating the suppressive views of a (minor but) "dominant" group. Also in this case the implied conclusion that "might makes right" ticks a lot of people off.