Why is that the responsibility of the conference? As far as I'm aware most conferences call for proposals to be submitted. Whether or not anyone of a particular group applies to speak at that conference is not necessarily a fault of the conference organisers? Are there conferences that actively seek out the majority of their speakers?
I am in favour of a wide variety of speakers at a conference (the more viewpoints the better), but this seems unnecessary. I would have liked for this to be a real conference though, the topics are great.