Ignore a User
One possible solution to the "black hole" problem would be to make sure that any time I share something with my "Family" Circle, I remember to also include my "Tea Party wackos" Circle so my uncle will still be in my loop without me having to be in his.
Another option would be to like my uncle. If I Ignore him, he is removed from my "People who have added you", and I will no longer receive content from him in my Stream , or receive any notifications when he mentions me in a post. He'll be able to see what I post, but for all intents and purposes he won't exist on my incoming Stream.
Well, mostly. , "An ignored person will still be able to comment on your public posts, tag you in photos, and add you to circles. You'll still receive notifications when an ignored person tags you in a photo. In addition, people you've ignored may appear as a suggestion again at a later time."
Still, it is better than Blocking him or removing him from my Circles because it is less overtly confrontational. Thanksgiving with the family will be much less tense as long as I pretend to have read some of his tripe--or just steer the conversation to how bad the Detroit Lions are playing.