Follow this line of thought.
1) Why women don't go to the events for everybody?
Because they are harassed and aren't treated as equal. They are uncomfortable, fear for the worse and don't feel welcomed.
2) Why this keeps happening?
The security is almost always not enough, or don't take the appropriate measures, or even don't care.
3) So the problem is within the security. Why not improve there?
Well... There are groups trying to change them, to reinforce them, but still you don't see much movement for the desired improvement. If you are not the organizer, the most you can do is shout for change and wait. This problem always existed.
4) Still, they don't need their own event. They are dividing everyone.
How? They wouldn't go to the other event. They aren't going already. They are doing something for their own that nobody did for them.
5) Still, they should fight for a better security and not doing something just for a group.
First, they are doing. Second, they can just have fun. Aren't they allowed that? Or should they keep fighting for something their whole life and never have fun in the middle?
6) They still are going with double standards. We can't hold an event only for men.
First, there is no need to. Second, you can, just don't be for the wrong motivations. Why would you do? Just because they are doing? Isn't that wrong? What will happen if you do this event? What will change for you or them? You could go to events before without a problem, but they couldn't. Why you don't fight with them for a better security, and let they have fun, instead of ruining their party?