Interesting responses to this question. Strangely, some are OK with an Internet tax if it goes to what they perceive as "worthy causes." Giving it to the cable companies so it can expand, though? Paying down the federal debt? Why would anyone want to give money to those who caused the fiscal problem in the first place? Rewarding them with money induces them to continue to be fiscally reckless.
Forcing a tax on the Internet, like all questions of supply-demand, will create underground black markets or "blacknets." I suppose if government is allowed to continue to ever-expand, it will use its newly-found tax resources to seek out and destroy those entities, and should the tax be high enough, we will regress towards how things were done before.
I can think of no better way than to cripple an already crippled economy.
The government should be in the business of safeguarding Rights, not figuring out new ways of taking our money.