Are you saying (and you are) that someone in Italy who wanted to advertise on a popular blog hosted in the U.S., should not be able to do so?
Yes. What's exactly wrong with that? If I bring three packs of cigarettes inside the EU, I will get fined at the border for evading something like 20 € of taxes, and my name will even end up into the list of smugglers. Even though the money was mine, and the cigarettes were made outside my country. Nobody has ever objected against that, because paying taxes is seen as normal. So if eluding 20 € of taxes is a crime, why should eluding 10 billion € be considered fair?
It's not like the person in Italy it not already paying taxes on his internet connection.
They're two different services, two different persons earning money, two different tax returns.
It's not like they would not pay taxes if they bought something from the ad.
It depends. If they buy them on Amazon, they won't pay a penny of taxes to Italy, thanks to the same Ireland-Bermuda trick, even though Amazon competes with italian sellers who do pay taxes and present comparable prices to the customers. It's a matter of fair competition, which certainly is very complicated to handle, but can't be dismissed altogether.