Pic and explanatory key at itmonline.org
There are lots of things we want to believe (partly at least because they fit our pre-existing shared ideas but just aren't true.
One topical example cited here by the scourge of bad science, Ben Goldacre, who writes for the Guardian newspaper under the handle, Badscience, is the Seratonin problems cause Depression opinion. Read on to see how we do our best to avoid the evidence and distort the argument.
Another thought that strikes me here is this: maybe it's not just a lot of individuals defending an idea they have individually committed to; maybe it's the group which shares the idea that's being defended.
What if the data was irrelevant because the idea itself is irrelevant? If what matters is the group's interest....