Vanquish is fine, they are not being sexist against women.
The simple fact is, the officers know that most of their members are nerds who couldn't handle women, proving the negative gamer stereotypes true. Vanquish needs this rule. Their members wouldn't function otherwise, once estrogen comes in.
It is sad, sure. But well, Vanquish has to work with the people they have. While it is unfortunate that those are people who could not function well in real life, they work well enough in the game for Vanquish to do something.
It is actually good for us women that this policy is in effect. Nothing is more annoying than playing with such pathetic losers. This way, we see what kind of players this guild has, and can go for guilds with more mature players, like the many guilds like that in europe that actually reek in world firsts.
We all win this way. Female players for finding guilds without such a high loser ratio, and Vanquish for actually being able to play without drama.