The easiest way to stop the crud is to ignore the kooks. There are other tactics as well. One is trimming the newsgroups or putting in a followup that takes out the group you want them out of.
Of course there is always the ISP route, but that takes time and a lot of complaints. It's not impossible however, especially when bot and flood attacks are used. The impersonation of supernews did not go unnoticed either.
Let's remember who brought this crap over here. This group was nice and clean till the idiot few from alt.binaries.pictures.autos xposted their crap over here in an effort to gain support.
I'd say to add that group back to every reply, but dropping to their level is not an option.