Comic con and all those festivals are all around the world--its a different demographic in each country so to stay that only caucasians attend comic con would be to ignore all the other countries which are multicultural. Star Trek had a variety of characters from all different skin colors, and although it might as started off with only white leads, it has always had a colorful cast.
Womens liberation as leaders in television has been silent for the most part, but there has been women lead roles in various shows from Dynasty to V, to Wonder Woman.
The fact is, women can be nerds.
You see this in shows like, The Big Bang Theory and in movies like, Hidden Figures. Yes! It's still a dominantly male social ladder but women are getting a piece of the pie.
As for white supremacists, that is another topic altogether.