Explicit fraud isn't that common, since it does have risks to the submitter that far outweigh the (limited) benefits of getting an extra publication on your CV.
I've got a stack of rejected papers that beg to differ.
> Isn't the point that they serve as a basic filter for obvious noise?
Yeah, and obvious noise is usually rejected. But sometimes it is not so obvious what the noise is, and that's why the scientific process is bigger than the peer review system.
> Isn't the point that they serve as a basic filter for obvious noise?
Totally, there is a lot to fix about it. But if you really want to put your effort into changing the system, I don't think you should focus on peer review. Destroying the business model of journals is where I would start.
You're mischaracterizing the system; it doesn't end with publication. After publication, the science goes out to a wider audience of scientists who can build on the paper or refute it if they find it's wrong. Sometimes this process can take a long time and many cycles of publicans, but that's just the nature of science.
We have to stop pretending like the peer review process is some kind of magical filter of true science, or that it was ever intended to be as such. That notion leads to the faulty idea that if it's published, it's true. Junk science gets published, even if it's not disingenuous, and that's probably true no matter how great you make the peer review system.