my ISP has partially blocked my Internet access twice due to suspected virus infections.
Virus is likely not the right word for things. Anyways...
There's really no reason an operator cannot run something like bro-ids.org and sink known bad traffic in real time. Yeah, sure, everyone will bitch at me. But it is operator fiat, and they're not sinking specific users, so well within common carrier exceptions on that aspect. No different than operators who block 'torrent' ports, smtp, etc.
Speaking of smtp, one could even redirect that into their system despam/clamav it and send it on its way. Better than nothing. Especially for the legit senders.