I think that depends on the scale.

If it is possible to get enough to leave such that the underlying community collapses, then it can work.

But if the effected population is 10%? 1%? If those individuals aren't in positions integral to the existence of the community?

If the 1% that left say the US were the "top 1%", then that would certainly cause waves, though I'm not sure it would completely dissolve the US. If on the otherhand the 1% that left were...hold on what's a 1% demographic..."everyone with rheumatoid arthritis", "those suffering from celiac disease", "people with natural red hair", "american indians", "chinese americans", etc then the US that remains is probably not a whole lot different from the US that was.

Brief research points to networks surviving random departure at rates as high as 50% (a random half of town folk leaving for different reasons) and loss of core individuals (healtchare/teachers/admin) at between 10-25%.

It seems there is indeed a threshold where collapse can be triggered by sufficient flight, and of course we've seen this in digital communities like digg.

I guess I'm just looking at like, if you're say a thousand racial minorities in an on average racist city of 100,000, and you all leave, the ratio of racists to non-racists will increase assuming the minorities aren't racist themselves. There is now less reason for the non-racists to campaign on behalf of the minorities because now there are fewer instances of injustice, and less reason for the racists to change their minds because they are less likely to engage in any racially driven encounters that give them the opportunity to change their mind.

I can see the appeal of leaving. You do the math, figure it's never going to change or won't change soon enough, the impact on your life is too great, leaving doesn't cost as much as staying does, and so you leave.

But suppose you've got lots of friends/family in the area. Elders you take care of. A neighbor whose pie is almost literally "to die for". The racism sucks, but your boss isn't racist and there's really only the one guy at work, so it's really just the subway that's a problem. Now staying is less expensive than leaving so you stay and make the most of it - vote to get someone like you on the city council, organize or participate in a support group, see something say something.

There is no one answer to fight or flight. It will always depend on the exact relation between the oppressed and their oppressor(s).