Discrimination (wether it be racial, religious, or based on sexual orientation) generally does not benefit the discriminator, it hurts all parties involved. In economic terms, discrimination is suicidal, because either (1) you're lowering the amount of customers or (2) you're hiring a less qualified worker over a more qualified one, and therefore are accepting lower productivity. Racial discrimination is a suicidal buisiness practise in a modern, multicultural society.
Racists do not benefit from being racists, unless the costs of being a racist are externalized via governmental means (a practise that should be opposed at all costs). As manifested economically, lessening the amount of people you sell to or hiring less qualified workers over more qualified ones, is suicide. In a relatively competitive atmosphere the heavy discriminators go out of buisiness by their own folly, and a boycott can help hasten their fall.
Let the discriminators shoot themselves in the foot. There is no need for affirmative action. The discriminators are imposing losses on themselves. Better yet, form one's own non-discriminatory buisiness in competition with them, and eventually watch as the people flock to your buisiness rather than theirs, since you are providing the service that the discriminators are refusing to yield to so many people. Hire all of the qualified workers that they refused, and watch as your firm's level of productivity outdoes theirs.
On the other hand, not all discrimination is a bad thing per se. What I mean by this is that we inherently must discriminate in terms of who we let into our own homes. If some random guy knocks on my door, and I don't let him into my home, I have "discriminated" against him, but obviously this is an entirely different thing than typical racial discrimination. Owning property inherently implies that you have discriminatory power over who you let use it; there is nothing inherently wrong with this.
Should it be illegal for me to refuse to allow someone into my home? I would hope not. Discrimination in itself is not a crime. Discrimination is an exclusionary judgement, and action taken based on such a judgement. Everyone has a right to discriminate all they like in terms of who they let use their own property. Even racists should be allowed to engage in the suicidal buisiness practises mentioned above. A valuable idea: all of us non-racists should band together and discriminate against them!
While discrimination in terms of one's own property cannot legitimately be illegalized, there is another type of discrimination, what I'll call institutional or external discrimination, that indeed should never be legal. That is, it is absolutely illegitimate for the law to require someone to discriminate in a particular manner, and it is illegitimate for the law to enforce discriminatory judgements over someone else's property. To decide who gets to use someone else's property is to make an illegitimate claim of control over that property.
As can be seen, the issue isn't really discrimination itself so much as property rights. The real question is who the legitimate owner of a given piece of property is. People can discriminate on their own property as they please, and it is not inherently wrong per se. It is important, however, to keep in mind that to discriminate too liberally in terms of economic relations with others will be to deny oneself the benefits of society. What people cannot legitimately do is (1) discriminate over someone else's property or (2) make discrimination mandatory.
In my opinion, immigration restrictions count as both of these follies. That is, laws attempting to limit immigration, crack down on employers hiring them and illegalize selling homes or other products to immigrants, falls under the category of mandatory and external discrimination. Indeed, laws illegalizing the hiring of immigrants and laws requiring landlords to evict immigrants constitute external and mandatory discrimination, and therefore they are violations of property rights (of both immigrants and citezens associating with them).
Furthermore, the economics that shows that racial discrimination is suicidal as a buisiness practise also has some implications in the area of immigration. For one thing, to turn down droves of willing workers from abroad is disadvantageous to local buisiness, who could very well use such employees. And to limit the amount of people in the country is simultaneously to limit the amount of potential internal consumers. Thus, if anything it is in the best interests of enterprenuers to have a steady flow of immigrant labor, and there's nothing inherently wrong with this.
Without resorting to such laws, a community that bars all immigration into it and refuses to sell products to immigrating people is engaging in a massive economic suicide. If there are other, more intregrated communities, and if communities are considered as being in economic competition with eachother, it is clear that the more integrated communities will out-compete the more separatist ones. While it would be legitimate for separatists to discriminate on their own property, if they try to do so on a large scale they will harm themselves in the long-run.
It seems to me that the incentives under liberty inevitably make way for a relatively integrated, not segregrated, society. Therefore, I am convinced that in an atmosphere of freedom separatism would be an uncommon practise, and to the extent that it is practised it would be at a considerable loss in comparison to integrated institutions and communities, and would therefore have an inevitable incentive to allow some degree of integration.
While my views on discrimination can be misconstrued by those on the left as being apologia for racists, I believe that to eliminate all mandatory and external discrimination, while allowing the separatist types to discriminate so long as it's on their own property, is the surest path towards an integrated society and quite a strong blow against racists because of the economics and incentives of the matter. On the margin, the separatists would effectively be forced to stop discriminating, or at least discriminate less.
Ultimately, separatists are trying to accomplish something that is impossible. It is impossible to manage to stop immigration in its tracks, and it is impossible to economically benefit while persueing a large-scale discriminatory buisiness practise. The movement of people of different ethnicities and nationalities across land masses is inevitable, and will only intensify over time. The integration of people, done on a voluntary basis, is a good thing that should be encouraged. On the other hand, discrimination on one's own property is legitimate. However, when it is done by buisinesses it is generally an anti-competitive buisiness practise, and thus there is every incentive in the world to not discriminate in such a manner.