Been a scientist for years. First you could read everything, then with genome technology and so on it became too hard to do it all yourself, then tried to digitize it and in doing so realized that our scientific knowledge as captured by private companies.
The scientific literature is one of humanity's great creations. Why don't you have access? Well, who controls the scientific literature? The scientists do it, the institutions support them, the public funds them, and the journals convert it to PDF and upload it. Who gets control? The journals! It's shocking when you think of it. If you ask "Who should be in control?" there's no way you'd come up with "the journals" as the answer. So we can put aside the moral issues and turn to why things are this way.
The scientific journal is about 350 years old, dating back to 1650. One of the first was Philosophical Transactions of the Royal Society. Their goal was a broad, educational one. But it got captured by big business and now it's very, very profitable. Margins of 40 to 50%. And how could it be otherwise? You give these people your papers for free and then buy them back.
Journals play an important role in scientific culture. They're key to the community of science, because they allow you to tell people what you're doing. They also do pper review, filtering/organizing, and are thus key factors in prestige and career building. None of those needs disappeared when journals went online. What going online did do was that it changed the economics of the business: the reaosn journals used to be a business was because it cost money to make copies. That's not true anymore.
But there are many costs of the old system. Only the wealthiest institutions get anywhere close to being able to access to all journals. Even at Berkeley, there are lots of things I want to access as part of my research that I can't get. I have to use a password to the Stanford system! And it's a hundred times worse for my colleagues at smaller institutions. And the general public gets hardly anything. If you find yourself with an obscure disease, you don't have access to anything. And scientists in the developing world face similar problems. I have a lot of colleagues in Argentina who have to get me to send them PDFs of things they need. Scientists and the public are being denied a huge tool in driving science forward.
When it comes to the genome, journals got tired of publishing long strings of AGCTs, so they forced it to be published in an online repository. These got used by scientists all over running computer programs. That led to the human genome sequencing project, because it became clear that these strings were useful. That's just one tiny bit: imagine if we opened the whole thing!
If science isn't in the public domain, the public domain has no meaning. But we still need scientific journals to do all the other tasks. The idea of open access is that those are costs of doing research. When you get a grant, it should realize that research isn't done until it's shared, so they should pay for publication. Midwifes play an essential role in the childbirth process, but it's absurd to let them own the baby and rent it back to the parents! So instead the open access system says do the same -- let science keep the results and pay a fee to the journals.
I was a reluctant crusader for this project, but when we saw the system was hurting our research, we had to take action. Our first attempt was asking the journals nicely to open it up. We quickly learned that was a mistake. Second, we saw the physicists had set up arXiv.org and bypassed the whole journal system altogether. A similar system was proposed for biology and met with such opposition that, under threats of Congressional oversight, it was defeated. Third, we decided to build an alternative system with the National Library of Medicine (PubMed Central) which put up electronic copies of all their papers. We figured journals would send their old stuff to the library, but again we were naieve. Most actively resisted it as "government control" of the literature. Fourth, we tried to use our power as scientists to pressure the journals to submit things to PubMed by promising to use the ones that did. 30,000 scientists signed this statement and we went to the journals with them. The journals replied "Screw you." Fifth, we decided to start are an alternative system: the Public Library of Science, a publisher that could show that prestigeous journals could be open.
What does PLoS do? First, we publish outstanding work -- keep the snobbishness and hierarchy so scientists won't resist. (And then we can change the model as we expand the system.) Second, we demonstrate the economic model works. Third, we can develop new ways to show why open access is important by providing for new uses of the scientific literature. PLoS Biology has become a legitimate alternative to the most prestigeous journals, and we've started PLoS Medicine and some more focused ones in computational biology, genetics, and pathogens. We've published 1731 open access articles so far. A drop in the bucket, but the start of a trend. All under a CC license.
The effects: most publishers now claim they're "open access", coopting the term (proof we're winning the PR battle). More importantly, government and funders are putting on the pressure. Still, many challenges remain. Many scientists are still reluctant to give up the old journals.