I don't think that's a very fair reading of what I'm saying.
First, whether something enters my filter bubble or not is not the same thing as the criteria I choose to look for new things, or to decide whether something stays within my filter bubble (say, a website I would add/remove from my RSS feeds). There's a passive/active dichotomy here.
Second, I don't think I've claimed there was nothing outside my bubble that wasn't garbage. Now, I do assume that 99% of the stuff out of it is, because that's the nature of the SNR on the internet. Note that all of that is of course entirely subjective, and I'm only talking about the value I derive from it personally.
Certainly, there are things that would be interesting that at a given time live outside of my filter bubble. But actively looking for them is not necessarily the best way to find them, as I might have to expend a lot of effort going through lots of junk before I get there, and other sources within my bubble might percolate that information faster, with less effort from me (say a link post on SlateStarCodex will give me a bunch of links to stuff I would have never found by myself).
Finally, I never said my bubble consists of all good information available, precisely because as I stated, all that information could not fit in anybody's bubble due to the limited nature of our attention or available time. So that's just a straw man.
The fact is that there's a game being played between what's inside my filter bubble and what's outside, and that game is not zero sum: most likely, actively trying to add more information from other sources will decrease the utility I get from it. It could be a temporary/local minimum (going through a bunch of garbage to find some hidden gem), but it could also be a more stable, lower utility state.