Maybe I am going to be wrong about this, but if Marshall decides to use a
light bulb as his example for something that lacks content but creates an
instant environment, does that mean I can take anything and apply these
principles? I guess everything in the world somehow has a "social effect",
but it must be dependent on the society, right? Because some cultures
still do not use light bulbs and wouldn't be subject to the light bulb theory
... but maybe they use fire, so does that count too?
Here's how I see it. MM cites the lightbulb just because he doesn't have to separate it from its message. It doesn't really have one. So it's easy to talk about it just as a medium. And as a medium, it does all those thing MM talks about. When you think about life before artificial light, you realize that, among other things, night was this huge fracking deal. Third shift? Are you kidding? People were just happy to make it through the night alive. There is this amazing book about the whole subject. So artifical lighting completely renegotiated our relationship with darkness. Work, family, schooling, the life of the intellect, sex, sleep. (For much of human history, towns and cities closed huge gates at darkness and sentries walked the wall, and you couldn't get in or you had the pay a toll to get in the lone gate. And it sucked if you mistimed your journey and got locked out in the frightening and completely dark countryside.) So MM says, think bout that, think about how the environment of human life changed because of this medium.
From there it is easier to understand how he views, say, the Kennedy-Nixon debates. What was said and who they were were very unimportant (to McLuhan and -- I think you would concede -- to the outcome) compared to the fact that they were on television. Television was the message. Therefore understanding television was, in a certain sense, more important and more predictive than understanding Vietnam or the economy. Because television renegotiated our relationship to so many things, including potential presidents. And people still don't get this. How many completely smart and reasonable people do you know who just cannot figure out why Dennis Kucinich does not do well in in national campaigns?