One thing to keep in mind is that the human mind isn't built to take in the thoughts of everyone at once, there would be an overload.
Ignoring that, in a perfect world, yes, a hive mind for knowledge would work, sadly this is not a perfect world. I would think that, because people are selfish and would not want their memories looked at for a variety of reasons, access to a person's mind, even a very knowledgeable person, would be limited at best. To get around this, I could see where there might be a database where such knowledge would be stored (like the web today) but as we are not dealing with a perfect world, you'd have to pay to have access to this, probably on a subscription basis, because where money can be made, you'll see someone trying to make it.
Another thought that came to mind is that there are several reasons that someone might not want their thoughts looked at. Assuming there is still individualism at all in the world of a hive mind (I can't see people willing to submit to the hive mind if there wasn't). How many times has someone gotten angry at someone else and thought of doing harm to that person? They may have no intent to follow through with this but they still thought it, and in a world where a hive mind is the other person could see/hear the thought and would see it as a threat, even though the person has done nothing at all save think and feel emotion, the other person would still feel threatened.
Look at a job like a diplomat, in a world that the other party could see into a diplomat's mind, the diplomat wouldn't have a chance of swaying the other party one way or another.
The entertainment industry would be completely gone, because you can just look into the minds of the creator's to be entertained. In this way there would be nothing left behind for future generations once the past ones have moved on and their minds are no longer connected to the link.
And if someone can access another's memories, how long will it take for them to be able to change it. True, if it was already on the hive it would take time to alter the memories of everyone, but I would not be surprised if it was eventually possible.
And now I'm just rambling, so I'll stop here. Sorry.