I think both approaches have value.
Consider this by comparison to the "war against drugs". One line of reasoning says "if there is no supply, there will be no market". Another line of reasoning says "if there is no demand, there will be no market". A third line of reasoning notes that with purveyance of such come a multitude of other social ills, and focuses on the "businessmen" in the trade: "if there is no way for supply and demand to meet, the market will fail."
Believe it or not, there is a market for spam. One person in a zillion actually replies to email claiming to be from the survivors of deposed African officials, resulting in them being able to fleece another sucker. If nobody replied, sooner or later they would get tired of sending the stuff. And yes, if they stop sending the stuff (perhaps as a result of going to jail), we won't have to deal with it. And oh by the way, a way to help them decide to not send it is to disable them from getting access to the net.
So, I say, consider spam to be fraud or theft of service when it is, and apply anti-fraud or anti-theft laws to the spammers. Consider it to be a costly nuisance to the receiver, and provide a way for him to inexpensively and reliably sort wheat from chaff (signatures and reputation services, which are not about "I signed my email so I'm cool" as much as they are about "I really am who I say I am, and you may apply policies as you see fit to deal with my email"), preferably without having to actually see the chaff. And yes, deny the spammer access.
Where this gets interesting is with so-called "legitimate spam". At least under US law, if you and I have a relationship as buyer and seller, the seller has a right to advertise legitimate services and products to the buyer. I travel in a vertical direction when I get spam from my employer; I have sat down with the designated spammer and have been told in detail that as a user of that equipment I am a buyer and they have a right to advertise to me, and take pretty serious steps to target and not annoy their audience. There is a part of me that wants to site in an 18" gun using their building as a target; there is another part of me that notes the photography in magazines and on billboards and the little jingles that go by on TV and the radio, and notices that legitimate advertising is in fact treated as (ulp!) legitimate.
In that case, they're not going to jail, and no ISP is going to refuse them service. I just want the ability to say "but I choose to not receive email from the designated spammer, and need to be able to reliably identify email from him in order to enforce that policy."
