I'm not saying it benefits the public necessarily, I'm saying it benefits those who opt for diversity. I don't expect STEM to have as big an impact on women's liberation as, say, business or politics. I don't think two cultures can be compared on this basis, my assumption is that, within one culture, diversified organizations will win out on average.

But diversity is only valuable to the extent that it helps create a better society. Like, ideally noone would even have to work! And there are plenty of examples of segregated (i.e. non-diverse) situations that we support becaues we deem them socially beneficial (e.g. sex-specific gyms and toilets, tall people competing in basketball, smart people are scientists, ...) (to be precise, personally I don't support these, but our society seems to, which would imply that the people on average do).

I think it depends in the task, and what the interest of the various groups are. If you have 10 engineers but only 2 of them are really passionate about it, and the other 8 would rather be doing something else, but due to incentives based on their minority status, they decided it was worth the extra money, you'd probably do a lot worse than a company which had 10 engineers that were all hired based on merit.