According to a study out of Yeshiva University, it's usually because of fraud. Now to be fair, the study is not linked, and the article does not suggest what percentage of papers are retracted overall, but they do suggest that the number, as a percentage of papers published, has grown by an order of magnitude since 1975. The study is also published by the NAS, which I would assume would usually be respectably peer reviewed.
Love to hear from Brian on this if he reads this site. My take is that if the methodology of the study can be defended, it is intuitive that we'd see a fair amount of fraud. After all, nobody gets tenure because they do work that defends the null hypothesis. There is a very real pressure to "show something new."
I have to wonder if it has a lot to do with requiring a Ph.D. to teach in most colleges (even freshman level courses that a high school teacher could lead), and a general "publish or perish" mood. If the study holds, I would not be surprised.
Another possibility is the strong push for full acceptance of evolution in bioscience; I do not have numbers, but I would have to believe the vast majority accept the hypothesis without reservation, and that a large portion of these have followed that with Richard Dawkins to atheism, or at least agnosticism.
At which point John Paul Sartre's comment about the nature of French existentialism comes to mind:
If there is no God, everything is permitted.
(in reference to Ivan Karamazov of the Brothers Karamazov)
And if you think that I'm enjoying quoting Sartre, as cited by "infidels.org", about the importance of Exodus 20:16 as it related to the scientific process, you would be entirely correct. It is absolutely delicious irony!
Attention, Rep. Norton! - It’s time to plug the loophole for registering Tactical RAM! If not now, who? If not you, when? For the children!
1 minute ago