Secondhand stupidity is a real killer.

[güey]

Could you please explain to me the emaning of the emphasized sentence?

Yeah, in 50 years, we're gonna have special areas outside buildings where you can use the internet. Internet designated zones, 50 feet from every entrance. "Don't bring the internet indoors. Secondhand stupidity is a real killer."

 

[Barque]

He's drawing a parallel between smoking and use of the internet. He's talking of internet zones like smoking zones outside buildings, and secondhand smoke (passive smoking).

 

[Barque]

To explain further, "secondhand smoke" (being exposed to smoke from others' cigarettes) is a common term for passive smoking.

He's referring to the use of the internet as secondhand stupidity, by which he means using the internet exposes you to the stupidity of others.

It's meant to be funny, not serious, so don't read too much into it.

 

[güey]

To explain further,

You explained it well enough in your first post.

 

[Tdol]

He also waves his arms around like someone trying to get rid of someone else's smoke.