During my brief time on Hubski, there's been a lot of touting of how Hubski promotes (or wants to promote) interesting and thoughtful discussions, and that people who don't want that shouldn't be on here.

I think the latter half of this thought is faulty. As you go on to point out, Hubski's unique mechanisms seem like they would certainly let a user easily insulate themselves from chaff. That being said, at the same time you're enjoying a high-brow Hubski experience, somebody else could be lording over their hub full of cat memes conceivably, to their followers delight. The two of you could never "run into" each other.

As far as comments in your posts or posts you follow, if Hubski wants to avoid the absolute disaster that is traditional moderation (see Reddit), the poster is going to need some sort of curation ability. Incredibly tough challenge as moderation, by implication and in practice often, can do the opposite of promoting real discussion. It is often abused and just used to stifle dissenting opinions. You see this behavior manifest naturally and also in the aggregate by Reddit user's abuse of the down vote. We know what it is intended for, and we know what it is actually used for in reality.