Matt, I totally understand where you are coming from -- a big part of my last job involved moderating the tens or even hundreds of thousands of comments we got every day at the newspaper where I worked, so I know what they can turn into. But at the same time, I think just turning off comments -- or handing them off to an invitation-only forum like Branch -- misses the benefits that can come from them.
Obviously not everything needs comments, and bloggers like you or Gruber or MG Siegler don't have to have them if you don't want them. But I think you need to realize you are giving up something as well as getting something in return. As Fred shows, a well-tended comment patch has real value, but it takes work.