Open Access: What’s the Debate?

I don’t know if I really understand the debate about open access.  Why is the goal of “making all scientific content available for anyone in the world” (from video by PHD Comics) looked upon in a negative light?  It seems to me that it makes everything more accessible, which would allow for advancement of scientific theory and approaches more universal/standardized and more streamlined.  Think about how many research groups around the world are working with the same molecule, theoretical framework, or structure.  There must be more groups working on the same idea than we realize, especially if we consider how much emphasis is placed on avoiding getting scooped.  How could our work get scooped if no one else is doing it?  Why would we be pressuring ourselves to publish results quickly or in journals with huge citation indices and reader rates if it wasn’t important for someone else to see?  If everyone’s research could be made public and readily accessible, it would reduce the redundancy and advance the ability to actually build on existing research massively.  What’s the downfall?  Why are we resistant to this?  Is there something I’m missing?  If science is indeed supposed to be about “discovering new things and spreading that knowledge around” (also from video by PHD Comics), which I agree with wholeheartedly, then why are we (as a community) impeding science by adhering to an outdated structure and resisting open access?