I think it is worth noting this form: http://craphound.com/spamsolutions.txt

And in short:

(X) users of email will not put up with it

(X) requires immediate total cooperation from everybody at once

(X) many email users cannot afford to lose business or alienate potential employers

specifically, your plan fails to account for:

(X) extreme profitability of spam

(X) joe jobs and/or identity theft

(X) extreme stupidity on the part of people who do business with spammers

(X) dishonesty on the part of spammers themselves

(X) outlook

and the following philosophical objections may also apply:

(X) whitelists suck

I would like to conclude that this is not some snarky elitist comment to this insightful blog post. I'm simply stating that spam is a very old problem, and many people have spent a lot of time trying to stop it. This form exists as a reminder that many of these options have been thought up before, tried, and found to fail. We've learned from some of our mistakes :)