This is what makes the situation profoundly more complex compared to other application of copyright, say in the software industry, where clearly switching to an open source model doesn't change the incentives i.e. who assesses the quality of software.
The long term effects on academia of switching to a model where the taxpayer gives money to scientists to pay for open access submssion of their research are hard to evaluate, and do no get enough though (imho).
That clearly doesn't mean that there aren't bad journals that are not OA, nor that for the benefit of the public some sort of arrangement shouldn't be found for older research: I'm a big believer in "faster decaying" copyright in general, and mandating that all publications describing research that is publicly funded become OA after, say, 30 years, would help significantly.