So if it’s wrong to consign someone to second-class citizenship based on skin color, why should we feel any more comfortable about forcing someone to live someplace horrible like Zimbabwe simply because that’s where he happens to have been born? ~Tim Lee

Because we’re not “forcing” someone to live in Zimbabwe (or wherever), but rather preventing him from living here.  Second, Zimbabwe was not always so horrible, and is not doomed to be so.  It is horrible for very explicable reasons of bad “policy,” if you can call systematic plunder and looting a policy, that are a matter of record, and which could be corrected if the Mugabe kleptocracy were no longer there.  I feel “comfortable” about stopping Zimbabweans (or anyone else) from coming to this country en masse, if they could actually manage it, because I see what this massive influx of refugees is doing to Zimbabwe’s neighbours and I do not want that for my country.  I would prefer that it not be happening to Zimbabwe’s neighbours, either.  The refugee crisis is a product of corruption and misrule on an epic scale.  The solution is not found in constantly offering maniacal despots a safety valve to release the buildup of social discontent, but in keeping the pressure on until the tyrannical goose is well and truly cooked by domestic rebellion.  Mass emigration not only drains other countries of some of their most industrious members, but it also serves as a much-needed relief for people in control of the sclerotic and bankrupt political institutions of many “developing” nation-states.  Western guilty consciences and the policies based thereon are their insurance policy and one of the means for their continued domination and exploitation of their subjects.  I have a hard time coming up with a moral theory that justifies that.

Update: On the subject of Zimbabwe, would you believe it if I told you that Zimbabwe was still 31st in a ranking of states for good governance in sub-Saharan Africa?  That means that there are 17 countries that are considered to be governed even more atrociously.  That seems worth nothing.