First: if scientists cared a lot about peer review, when their papers got reviewed and rejected, they would listen to the feedback, do more experiments, rewrite the paper, etc. Instead, they usually just submit the same paper to another journal. This was one of the first things I learned as a young psychologist, when my undergrad advisor explained there is a “big stochastic element” in publishing (translation: “it’s random, dude”). If the first journal didn’t work out, we’d try the next one. Publishing is like winning the lottery, she told me, and the way to win is to keep stuffing the box with tickets. When very serious and successful scientists proclaim that your supposed system of scientific fact-checking is no better than chance, that’s pretty dismal.
Second: once a paper gets published, we shred the reviews. A few journals publish reviews; most don't. Nobody cares to find out what the reviewers said or how the authors edited their paper in response, which suggests that nobody thinks the reviews actually mattered in the first place.
And third: scientists take unreviewed work seriously without thinking twice. We read “preprints” and working papers and blog posts, none of which have been published in peer-reviewed journals. We use data from Pew and Gallup and the government, also unreviewed. We go to conferences where people give talks about unvetted projects, and we do not turn to each other and say, “So interesting! I can’t wait for it to be peer reviewed so I can find out if it’s true.”
Instead, scientists tacitly agree that peer review adds nothing, and they make up their minds about scientific work by looking at the methods and results. Sometimes people say the quiet part loud, like Nobel laureate Sydney Brenner:
I don’t believe in peer review because I think it’s very distorted and as I’ve said, it’s simply a regression to the mean. I think peer review is hindering science. In fact, I think it has become a completely corrupt system.