I would like to see more diversity. Not just in terms of demographics (though that too)

To take a stab at that applause light.

Ceteris paribus yes I can agree diverse contributors may be beneficial to our mission. Especially value diversity, since differences in desired conclusions may lead to motivated cognition being called out more. But I think when most people speak of diversity they don't have that kind of diversity in mind. So sticking to the other kinds, I have to note that I haven't seen a single data driven argument for this why this would be so in actual humans. It is simply assumed or asserted. I'm pretty sure this is so because it happens to be a sacred value of our society. While cyberspace is clearly different from meatspace, studies done in meatspace seem to show diversity has negative effects that are seldom talked about.

But leaving aside such undesired consequences let me just point out that the ceteris paribus in my first paragraph is also unlikely. Very small differences can result in almost complete homogenization. Not only has it proven difficult, expensive and perhaps mostly ineffective to do this in meatspace, you would actually need to keep a delicate balancing act to keep a certain heterogenus mix together if your goal isn't to simply swap one group for another. I think we already spend insufficient attention spent on gardening and this would be just one more difficult task to add to the list.

Once more I ask why no one ever subjects such proposals to explicit cost-benefit analysis?