Well yes, but sometimes you can throw out the wheat with the chaff when you do that; sometimes threads recover after a troll has had their say (I don't use Google Groups).
The SNR in u.r.c. has dropped to about 10% once you take out the trolls, the flames, the responses to them and the "don't feed the troll" bleating. I do think Usenet has pretty much had its day, which is a shame - it was a fairly global community, whereas forums tend to be left- or right-pondian.