Perhaps we should start with things like falsifiable predictions, a logically-consistent analysis, etc.
Again, the scientists who study these matters seem to think there are falsifiable predictions and that the data support previous ones - like Jamis explained, there may be reasons why they fabricate these beliefs apart from scientific study.
I do find it a bit hard to accept that universities all over the world, staffed by people whose jobs can't be taken away, have bought into the conspiracy so wholesale that they refuse to poke holes in the existing work. You'd think someone would, and that some of his peers would join in, well, sort of like the conspiracy that supposedly led to the global warming theory.
It's not like debunking warming is without it's own grants and finders - look at how much money the energy companies and political parties spend on debunking it.
Why has all that corporate funding failed to generate any significant disputes in the scientific community?