I don't see how it is any different then something like back country skiers, or base jumping. There are is a wide spectrum of risk in a lot of "extreme" sports.
Not trying to make this an attack either, I just see a lot of parallels elsewhere in other sports -- and it seems a little hypocritical to me that the climbing community would even be divided over this.
Furthermore, sticking with the BC skiing example, many people (resort skiers) would see it as irresponsibly risky. But we know that BC skiers take all the preparations they can, from monitoring avalanche reports and forecasts, taking training classes, learning how to probe and escape avalanches with partners. Similarly, Alex very much spends a lot of time preparing for his free-solos, in all aspects of planning -- which makes it much more calculated then "irresponsibly" risky to me.