Ty,
Something I had to learn about back when I was running a public BBS was something called the "AOL Ruling".
If you monitor and control the content of a BBS, a chat room, a forum, a mailing list, etc. then you are responsible for what is in that channel, even if you didn't catch it. If you do _any_ monitoring or filtering, you become responsible for _all_ of the content.
If you _don't_ monitor or censor it, then you are not liable for any illegal content there (it is understood that you will remove anything illegal if notified of it).
This is why TW and the rest of the providers are taking a "shotgun" approach, whether it's removing all of the "alt" groups where the majority of offenses are found, or removing the whole thing.
As to running a Usenet relay - it's a very expensive thing to do. It's a LOT of data and a LOT of traffic. Most usenet servers, I believe, are still run on multi machine clusters. This is why subscriptions are so high, why ISP's are eager to shed the burden, and why you don't find local guys who used to run BBSs running their own Usenet servers.
Compared to the amount of benefit that any small group of users like our LUG would get, the traffic of a Usenet server would mostly be wasted - but it would cost a lot.