You're equating a physical reality with a virtual one. The whole of the Internet is about filtration. There's no "real" location that grows worse or that requires effort.

Besides, a per-site filter won't stop offtopic posts from being flagged, or debates from starting. They'll only allow certain people to ignore certain posts, which those people want to do anyway. I for one wouldn't block TechCrunch, and I'm certain many more would keep reading it as well.