"Imagine a world without free knowledge" -- if that means a world without Wikipedia, well, it would be like 2003. Even if it meant a world without the web or the internet itself, it would be like 1994.
We haven't gotten any richer, happier, or more productive since either date, so really who cares? You'd lose the minor buzz you feel from visiting your favorite sites, but they're more than replaceable in the real world.
The main reason people freak out so much when pondering the disappearance of the internet is that we live in an age of cocooning, and they're too dismissive or fearful of those real-world substitutes for farting around on the Facebook etc. They really would have nothing to do.
As for Wikipedia, it is incapable of increasing our wisdom, for technological reasons alone (forget who controls and edits it). It belongs with websites that only allow you to tunnel narrowly around an initial search, rather than browse broadly -- Amazon, Netflix, iTunes, Google, eBay, Pandora, and any other site that has so massive a scale of items on offer that you cannot hope to browse through them.
You must instead tell the search bar where you want to go, and trying to click away from that target will still keep you confined to a narrow range around where you started. Similar or related items, customers who like this also like that, also by this artist, and so on.
The best they can do to expose you to things you didn't even know about is to have a "featured item" or "new items". That's like the movie being played at a video rental store -- better than nothing, but not as good as browsing their selection.
A real encyclopedia allows browsing. In fact that's what you end up doing most of the time after the initial stage of "Oh I wonder what it says about this, Oh I wonder what it says about that!" That's true whether it's a general one or a subject-specific one. So browsing is fractal -- an encyclopedia only about animals still allows you to explore parts of the animal world you didn't even know about, and so could not have purposefully searched for.
In high school I had a Benet's Reader's Encyclopedia that I used purposefully as a reference for a little bit, then quickly switched to just flipping through pages at random and following through on the entries that sounded cool. Blind variation and selective retention -- the basic ingredients for evolution by natural selection. And you just can't get that first part with massive-scale sites based on a search bar.
It's not as though a person couldn't tunnel before if they wanted to; all of the specialized knowledge in Wikipedia is out there in books or databases. It's just faster and sometimes cheaper to access through Wikipedia. I use it for the #1 songs on the Billboard charts, to familiarize myself with the zeitgeist over time. But I could find that out some other way, though it might take a couple days instead of minutes, and maybe cost me something, though nothing prohibitive.
So in exchange for a tiny boost in convenience -- remember how well-run and productive society was before the web -- we've sacrificed the ability for our sight to wander into places we didn't even know were there. The search-and-tunnel websites make our view so hyper-specialized that we often cannot see what is right under our nose.
We try to make the best out of the internet, now that it's here, but it would probably have been better if we hadn't adopted it in the first place.