The prevailing moral judgement is that excluding people from a group because of inflexible factors (like gender) is a bad thing.

Because its a moral judgment, we can assume that even if monocultures are functionally superior with regards to performance we still will prefer a diverse culture for the intangible benefit of 'good ethics'.

Heh. This brings to mind the thought that a diverse culture is likely to produce monocultures. If some Indians develop a new game, then you'll probably end up with mostly Indians playing the game--if it takes off, then people from other cultures might start playing the game, but the best and the "serious" players would probably be Indians. Even serious non-Indian players would probably pick up more Indian culture than they transmitted their own culture to the sport, and it would at least be very slow to diversify.

No, wait, it occurs to me that "some Indians" would require an India, and therefore a kind of monoculture there to start with. Perhaps a "diverse culture" would mean there is no India--there would be equal proportions of all conceivable backgrounds and stuff everywhere, or at least something close to that.

But, now, wouldn't that society be a monoculture? A very serious monoculture, with the vulnerabilities that go with it (i.e. lacking the defenses that come with diversity). To give an example: if every city looks the same and has the same number of each kind of building and uses the same proportions of transportation methods and so on, then if a virus gains a mutation that makes it go very well through a particular kind of transportation, it'll be able to infect every city equally well. The situation goes from "virus no one cares about" to "virus able to infect everything". On the other hand, if you had rich cities in which one type of transportation dominated, poor cities in which another one dominated, some cities that were hubs of international travel and others that rarely got any visitors from more than 15 miles away--then you'd go from "virus no one cares about" to "some cities overrun, others barely affected", which makes it much easier to leisurely prepare a response with aid from the barely-affected cities.

(Genetic diversity is good for fighting disease, for similar reasons.)

Mmm, I have reached the conclusion that the goals of diversity at the level of individuals found in a group, and diversity at the level of groups found throughout civilization [you could define any number of group sizes if you wanted], cannot be simultaneously achieved to their fullest extent. If you have no monocultures, that puts some limits on how diverse your set of cultures can be. This meta-problem gives me a kind of zen feeling.

Because "community" is a bit of a misnomer here. We are talking career development, not book clubs. I can afford being excluded from a book club but I need to make money. As such, I can't afford to be excluded from career-making-or-breaking networking groups, conferences etc.