While I'd agree that (at least for some people) the outgroups' social group would become a bigger issue during encounters, I would argue that the familiarity brought on by that hypothesis would not only reduce the number and size of "outgroups", but also reduce the number of people who would react negatively to "outgroups," as well as their susceptibility to race/nation/etc-based propaganda (which, interestingly, your 2nd link seems to suggest)

Anyway, while I think there's some truth here, I do believe the benefits far outweigh the costs - in this instance, but also for the Internet in general, when you consider the other benefits (and risks of course) it brings - accessibility to education, for example.