Who's to say that whatever people were doing with that time before was doing something significant "for the collective human experience"?
http://en.wikipedia.org/wiki/Pleasure_center#Experiments_on_...
The worst part of these games is that they can act as a surrogate for success: your life may not be progressing in any way whatsoever, you may have goals and aspirations that you are not pursuing, but you are getting rewards and constantly progressing in a game - I'm not sure how good our brain is at distinguishing between real and virtual rewards (especially when the virtual rewards are guaranteed, but the real rewards are... well... hard).
http://en.wikipedia.org/wiki/Reward_system
All this is to say: other potential time wasters (TV is probably the most common) may be less likely to cause addictive and/or harmful behavior (I can't believe I'm arguing that TV may be less harmful than video games, but there it is). Sure, the majority of people can play causal games strictly in their downtime, but for some it spills over into what may otherwise be productive time, and for a relative few it can take over (where do you think Zynga's revenue is really coming from?)
http://www.pixelpoppers.com/2009/11/awesome-by-proxy-addicte...
Most "normal" people waste the majority of their leisure hours, depending on your definition of waste. The audience here, however, is not typical.
I'm 'wasting' time right now skimming this article, reading this thread, posting a response about how i'm wasting time right now.
The difference is that I think it is interesting to read about failing software startups with billions of dollars invested in them. So it is atypical with regard to subject matter. I have no interest in american idol or tom cruise or Oprah or glen beck.
I also find that I am most productive at programming when I approach it as a fun game that I am 'wasting time' at.
(apologies for going meta).
http://www.allfacebook.com/11-have-had-sex-with-someone-they...
It happens. If it gets you laid, it sure is making the world a better place.
Also, it's sometimes hard to distinguish something new and valuable from an idle waste of time. As my dad says, you never know which cloud is going to give you rain.