hm .. sounds both like a US-centric issue, and also indeed the focus.
In Europe, esp. German-speaking countries, I do not really know of any kind of venue / location that is strictly non-alcoholic.

About the focus: Events I organized in the past, including the Webmontag Karlsruhe, had their focus in networking, not getting drunk as a skunk. So the venues were primarely selected for their ease of networking, socializing, arrival and maybe food (vegan / vegetarian option is always a nice touch). As locations go in Germany, none of these were without alcohol, but they weren't what one would call "party" locations, but local pubs / inns, restaurants, and the like, with the option for a separate room or at least off-space corner / tables.

So, back to topic: "Should WordCamp Afterparties be alc-free?" - Nope, as long as the focus is PRIMARELY on networking, not excessive drinking. If I want to go on a drinking spree, I've got enough folks spread all over the world to go party with - wouldn't want to do that as an "afterthought" of a WordCamp ;)

cu, w0lf.