Marriage has as one purpose to support the community from which it arises. Inter-racial marriages normatively cannot do that. Indeed, the only community that inter-racial marriage supports is a multi-cultural cosmopolitan community. Now we can pretend that is not true that inter-racial marriages do not normatively support the community wherein it is located but we have only to lift our eyes to see how our social order is fracturing. One reason for that (not the only reason) is the proliferation of unequally yoked inter-racial marriages.
Concerning Ruth
In my defense though I’m also bigoted against marriages contracted between people coming form vastly different classes, vastly different cultures, and those who have a vastly different health status. Call me silly, but I think those entering into marriage should have as much in common as possible and I am bigoted against marriages about to be contracted that find the differences to be significant and doubtless abiding.
“It was called Babel.”
And Babel bequeathed its legacy of imperial ethno-mixing to the transnational empires that followed in its footsteps. The Persian empire that succeeded it, for example, was abhorred by the Greeks partly because they knew about this aspect of despotic Oriental rule. In his last major dialogue, The Laws, Plato put it this way, that this kind of loss of racial identity would have been the lot of Hellas too, if the Greeks had not been able to repel the forces of Xerxes:
http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.01.0166%3Abook%3D3%3Apage%3D692
“Many are the discreditable charges one would have to bring against Greece in relating the events of that war; indeed, it would be wrong to say that Greece defended herself, for had not the bondage that threatened her been warded off by the concerted policy of the Athenians [693a] and Lacedaemonians, practically all the Greek races would have been confused together by now, and barbarians confused with Greeks and Greeks with barbarians,—just as the races under the Persian empire today are either scattered abroad or jumbled together and live in a miserable plight.”