Why is it so vital to classify stuff as "garbage" and "non-garbage"? (The fact that you chose to use the word "garbage" with negative connotation says a lot.) Good stuff gets looked at, the rest (shallow self-promotion, astroturfing, libel, etc.) gets corrected if it's something a lot of people will run into. Given the cost of running Wikipedia already, it's not like a few tens of thousands of pages is going to make a difference in a digital world.
The thing I loved about Wikipedia back in the day was the ability to find obscure stuff. Yeah, I could search for it online, but that didn't give me the context. It was a real joy to just lose yourself reading links in Wikipedia. But, after seeing a bunch of articles I care about get removed, it's less of a joy because I have to wonder what other information was deemed "not notable" enough for me to read.
The ultimate problem with "deletionism" is that people with no real knowledge of the topic are often the ones calling for deletion. Or, worse, you get someone who has a personal interest in deleting an article as "revenge", as in the case of the Old Man Murray issue from last week.
Here's my "faling out of love witih Wikipedia" story: An article on "Dragon Kill Points" (DKP) was deleted back in the day by someone who thought it wasn't notable; as a respected MMORPG developer, I argued it was a very notable and important concept to the field. I managed to help put off two deletion attempts on the basis of "not notable" in the span of a few months, only to have the article deleted later in a "speedy" process. The first two proposals came from the same person (after the first one was an unambiguous "keep" result), and the three requests came all within 4 months of each other. This seems a bit beyond someone wanting to "clean up" the site. Of course, the article was added back some years later, but it's a shadow of its former self and not nearly as useful.
Lesson learned! Not is a lot of potentially useful information missing, I also learned that anything I contributed in my field might be wiped out by someone who just doesn't like it. I'll spend my time doing something more useful than contributing or using Wikipedia, thanks.