Sappho, you keep stating that you can't learn social skills on the Internet, and this strikes me as, unless one holds a very specific and narrow definition of 'social skills' distinctly untrue. The Internet's mode of communication has its own set of social skills, one with a significant overlap with that of face-to-face. There are absolutely skills and cues one acquires speaking on the Internet. You've mentioned yourself that you know people who are perfectly nice in real life but entirely unreasonable online; these folks haven't built up their online social skills (and this ties into my point from my previous post about having less of a problem with Facebook and more of a problem with people misusing Facebook)
I think the crux of my argument is that face-to-face social skills are not the be-all and end-all of social skills. Society continues to function as more and more interaction is facilitated by technology, and I don't think this is a bad thing. I'd point out that the widespread acceptance of and reliance upon telephones, both landlines and later, mobile (cellular for all of y'all Yanks) didn't exactly result in society crumbling to its end, and whilst it did change things, change is about the only thing one can count on (disregarding, of course, death and taxes).
Debate will survive in the same way any art form survives; it may no longer be necessary to life or social standing (and I'd argue that the social skills used in debate transfer exceedingly well to the online format; see: this entire thread) but it will remain as a hobby or a sport, much as, say, ballet or hunting (in much of the richer areas of the world)
Finally, you're discounting the sheer amount of time the youth of today are just about required to spend in a face-to-face situation, be it at school or jobs (which, for the youth, at least in the first world where online media is having the biggest effect) tend to be retail positions which necessitate constant human interaction. Before social media, (or rather, telephones) a lot of the time outside of school hours was spent alone, and whilst face-to-face meetings were probably more common then, out of necessity, plenty still occurs now, (and I doubt it's any significant amount less than has been happening for the past ten years - if this were going to cause huge issues, we're a bit late on the uptake)
To summarise: Online social skills are not inherently inferior to face-to-face ones (and there is a significant overlap between the two), if face-to-face communication were going to be made obsolete, we'd have seen much greater catastrophe earlier, as phones came into the mainstream, things like debate aren't going to fall into disuse, even if the need for face-to-face contact were to be entirely obviated, in much the same way as, if an artist sells a painting and gets enough money to eat for the foreseeable future, he does not stop painting more, and finally, the huge increase in opportunities for social interaction provided by social media (and earlier, telephones) has resulted in an overall increase in social interaction, which is not, when one phrases it that way, a big surprise.