Be that as it may, in order to assess the quality of a community-driven site, one has to place value judgements on its content. Sometimes these value judgements fall short of perfection, but they're necessary and unavoidable.
It is interesting that you raised the prospect of filters yielding false positives. If you were talking about my judgement as an individual, then I'll admit that I'm blinded by the human condition, but I'd like to point out that I relied on blanket labels to avoid getting into a discussion of minutia of specific posts on Reddit. If you were referring to filters integrated into the software we'll use for our startup, our approach to avoid the "garbage" (we can agree that there is garbage out there, and avoiding it is a good thing, right?) is to narrow the focus of the site, rather than to build in karma-based influence restrictions and enhancements of individual users.
Hopefully I'll be posting a link here fairly soon, so all of my vague mumbo-jumbo will make more sense, and it'll take less imagination to see how our site could be used for negative purposes and how that might be limited.