Vigilante Zombie Killer Disinfectant
YES- Most users are really, really dumb... get over it and fix the problem.
Since so many people are too stupid to prevent their computer from being infected or incapable of doing so, I believe it should be the responsibility of good netizens and ISP's everywhere to fix the problem for them. The increase in available bandwidth alone would pay for the effort.
These people do not even need to know that their computers have now become "disinfected".
Since it is possible to see the Botnet traffic at an ISP level, the ISP should simply hack the client's pc and install appropriate software to remove the zombie infection and prevent re-infection.
There are plenty of freeware solutions that will solve 98% of these problems, except Grandma/Grandpa/Etc would not know where to look for them and how to install or maintain them. All totaled it could be a 10 to 20 meg download for Malware Bytes, A Squared, Spybot, Avast, Zone Alarm, Combo-Fix, Hijack This, etc. Most will auto-update without user interaction.
Many of these software companies provide their freeware versions because they recognise this service must be provided for the greater good of the world internet community and that they will get paying customers in return.
All the ISP has to do is change their terms of service to say that they will occasionally scan a customers PC to make sure it has appropriate malware/spyware and anti-virus protection and that it is up to date. If the clients PC is spewing spam or other more nefarious crap, they either get fixed or shutdown.
The PC would get redirected to the download page after the scan closed and removed/killed the active infection. The proper software would be installed, rebooted without user interaction and a deep scan performed.
This process would be entirely legal if proper notification was provided when buying or renewing internet service.