I think libertarianism offers the only tenable approach to global ethics... While it's not without problems, it's certainly less problematic than other left-leaning approaches. Home-base consists in "self-ownership," the "non-aggression axiom," and universal voluntariness. In terms of global issues, libertarianism, embraces a non-interventionist foreign policy and global free market capitalism.
For libertarians all universal human rights are negative rights. That means that global ethics is more about what you "ought-to-not-do" than what you "ought-to-do." Ultimately, there's only one universal moral rule... the "non-aggression axiom," which states that individuals (and groups) are absolutely forbidden to harm others, except in self-defense. The argument for free markets goes like this: if it is true that I own myself, then (logically) I own the fruits of my labor. So if you unjustifiably use coercive force either against my body or my property you've violated it and I have a right to protect myself and my property. If I willingly give you my property or sell it to you...there's no violation... even if it's a bad deal. In short, if you get "suckered" into a bad deal, its your own fault. Call it the "buyer beware principle." Thus, even, if you willingly sell yourself into slavery for a mutually agreed upon amount of time, in exchange for some other good or service (or out of beneficence) ...that's fine too. However, slavery is (almost by definition) perpetuated by force (or threat of force) and rarely (if ever) voluntary. Although, you have a right to voluntarily sell yourself into slavery, I have a "right" (if not a "duty") to point that it's a bad deal. But I can't use force to prevent you from becoming a slave. If you have an extremely low IQ, if you're an underage child, or if you are suffering from a mental disease, some libertarians (J.S. Mill) might paternalistically intervene, at least temporarily. I might intervene just long enough to determine your rational status, or just long enough to point out that it is irrational.
The non-aggression axiom also applies toward cultures. If your culture has a rule that says that it's OK for men to sell adult women (or children) into slavery without their consent...then that culture violates the non-aggression axiom. The problem here is that in many cultures, women willingly allow men to sell them, because they believe that their God created them to serve males. So what duties does libertarianism impose upon us as observers of culturally-induced harm to women? I might present those women (and men) with compelling rights-based and/or utilitarian arguments in favor of female equality. But I wouldn't be very optimistic. We all know that culture (especially religious culture) can be a powerful liberty-limiting force in the world. However, I would argue that we libertarians (individually and collectively) are morally bound to NOT advance the interests of any aggressive individuals or cultures; that is we have a negative duty to not cooperate with aggressive persons or cultures. We also have a "negative right" (based on freedom of speech) to point out that individual P and/or culture X violates the non-aggression axiom and is therefore immoral.
Now what if I convince a particular woman (or a group of women) that servitude is morally wrong and they REQUEST my assistance in either escaping from an aggressive culture or transforming it into a non-aggressive culture? As a libertarian I can choose to either assist or not assist, based on how much I'm willing to risk in providing that assistance. If I could (in fact) free those women by donating $1000. to a certain private military group that defends women...I might do it. But remember....it's my money, my time, and my effort. In short, I do not have a positive duty to intervene in terms of either speech or actions. Now if I promise to intervene, I must keep my promise. Now the hallmark of left-leaning morality is the idea of positive legal and/or moral rights. However, thoughtful libertarians observe that there are many ways to intervene short of violating the non-aggression axiom. And that if we employ aggression in order to stifle aggression we perpetuate more aggression, toward not only the persons or groups that we intend to help, but also pose risks for the intervener. And, of course, there are so many aggressive cultures in the world, we can't intervene in all of them without going bankrupt. Therefore, a rational libertarian will intervene only in those cases where there is a probability that intervention will succeed...and not make things worse.
OVER-THE-LONG-RUN the best libertarian strategy is to teach all individuals and groups in the world to accept the non-aggression axiom. But we, obviously, can't force everyone to do it. The problem with liberal statism is that governments often intervene in cases where aggressive intervention is futile, and likely to make things worse. Minarchists like myself argue that aggressive political intervention (especially within civil wars) almost never yields a positive utility ratio. Therefore, we advocate non-interventionist foreign policy. But that doesn't prevent us from engaging non-aggressive intervention.
As non-aggressive culture spreads throughout the world (via teaching and learning) aggression will (eventually) become less common, and ultimately extinct. But remember...we libertarians can't engage in non-defensive aggression, but we must actively refrain from supporting aggressive individuals and cultures. That means that the non-aggression axiom prevents us from advancing the interests of aggressive individuals and cultures. Now I might forge a defensive agreement with certain individuals or groups and promise to defend them from aggression, but libertarians must be leery of pre-emptive defensive strikes.
In sum, libertarians cannot support the mantra: "When in Rome do as the Romans do." The libertarian manta would be: "When in Rome, do as the Romans do...but don't harm anyone; even if its legal and/or moral in Rome." Better yet..."Don't go to an aggressive Rome, unless you're going to crusade against aggression." So if you own a multi-national corporation, and have employees in Rome who are victimized by an aggressive culture, you cannot support that culture. If you choose to teach them non-aggression, the host culture (or government) probably wouldn't like it. Nevertheless, we libertarians have a negative duty to not assist in the advancement of aggressive individuals or groups. So, if you want to assist the world's poor...do it with your own money...or with money voluntarily contributed by other like-minded individuals and groups. Governmental interventions that use tax money is immoral because involuntary taxation is a form of theft, and because state intervention rarely works. One final note on legality... Libertarians are (at best) minarchists, and therefore oppose the expansion of national and international legality. Our policy is to advance morality, which is limited to advancing non-aggression. In short...you can't force people to be good. And finally, being good is about what you "don't do." Don't kill, don't steal, and don't break voluntary contracts. Ant thoughts?