I'm against these, because I'm against gender discrimination. Gender discrimination means that one gender is treated differently from another. It's also interesting to know whether transwomen will be allowed. Some radical feminists only accept 'born as women' to their conferences. And if transwomen are accepted, what's their definition of that.
As a society, we accept discrimination in order to build a better and more equitable future.
SV prides itself on being a meritocracy, but it isn't a perfect one. People were born with money and connections have it much easier than the average schmo off the street. But certain minorities in our field* also have the added burden of having to battle pervasive stereotypes that sometimes borders on downright hostility on top of a near complete lack of a support network.
In order to become a more perfect meritocracy, we should strive to level the playground for everyone, but we can't easily tilt the playground such that average schmo's are on equal standing with people born into SV royalty, but we can make some minor shifts to help overcome the burden of being stereotyped because of what you look like.
So we accept some discrimination. And we benefit from it. The fact of the matter is that having diversity in startups is A Good Thing and increases the odds of success (unless your plan is to only sell your product to people who look/act/think just like you).
* Yes, women are the majority in the world, but for this and all discussions, it is important to limit ourselves to a field; in this case, tech startups. I would be just as supportive of a conference/support group/etc. for promoting and helping male child care workers (95% female) to overcome the stereotype of men being unfit for child care.