Wow, I was unaware of this issue (maybe because I don't go very often to conferences and even less often to afterwards gatherings?)
I guess most people (including myself), male and female, have received "unwanted attentions" at conferences and elsewhere, and that is probably part of the human nature and (although not fun) it could be ok.
But from "unwanted attentions" to plain harassment and the facts described here, it's a huge step in wrong direction. These facts are not acceptable at a tech conference (well, they are not acceptable anywhere).
I'll surely check if there is a policy for dealing with harassment in any conference I'll attend in future, refraining from attending ones that don't, and mentioning the reason to the organizers.