Site administrators use CAPTCHAs to prevent automated scripts from performing certain functions, such as creating an account, sending email to a distribution list, or participating in a discussion thread.

That's fine, as far as it goes. But, frankly, I'd also like to see certain people on the Internet prevented from doing certain things. You know, like: logging onto the Internet.

And so, a modest proposal: Internet Access Captchas, built right into browsers, designed to greatly reduce the overabundance of youtube commenters, Facebookers, and Twittererers.
Here is my prototype:

Hello, and thank you for your interest in The Internet.

Please type the correct sequence of characters into the field below.

"Will the last person to abandon USENET turn the lights when they leave?"