Thi Chi,
Cremo does not make the case for scientific "purges." What he's talking about is the filtering of information which must happen. Usually it happens because of advances in understanding. That's why we no longer learn about the ether in physics. Lord Kelvin caused serious concerns about evolution with his estimate of the Sun's lifetime. But that turned out to be incorrect because he (and nobody else) understood quantum mechanics and nuclear physics. However, we can still go back and find the original papers and, as Cremo did, the actual evidence.
Now, it is impossible to rebut Cremo on a case by case basis without putting a huge amount of effort - equal to that taken to write his book in the first place. Nevertheless, Cremo has made an extraordinary claim - namely that there is a de facto conspiracy to ignore evidence that would call much paleontology and evolutionary theory into question. What I'm missing is why would people do this? As methods get better then it is routine to discard old theories and produce better ones. Witness the development of quantum mechanics. Nobel Prizes and such are associated with such paradigm changes. If someone could prove that humans co-existed with dinosaurs then I have no doubt at all that they would be widely feted. The problem is with the proof. Cremo has to demonstrate beyond doubt, using reproducible scientific techniques that his conclusions are correct. He has not done that and at least some of his findings have been given serious attention and shown to be mistaken (e.g., the blue metal spheres). Now he would argue that these requirements are part of the conspiracy but they aren't. A hot young assistant professor at Harvard would give his or her eye-teeth to find proof that humans were around when Cremo claims. In fact, he or she would likely sell their grandmother into slavery to get such proof - it would be that exciting.
So, we must examine Cremo's legitimacy since he doesn't have scientific evidence; The first thing is that he has an agenda, which is what he is claiming about evolutionists. However, history shows that scientists are much more willing to abandon theories than religious people their beliefs. Secondly, Cremo i smaking money from his books which are designe dto attract the attention of a certain segment of the population. That is religious fundamentalist types who usually have little scientific background and also have an agenda, even if only a personal one. Thirdly, Cremo included at least one citation to Weekly World News which is unforgivable. How can anyone be taken seriously if they do that.
So, what it boils down to is that Cremo has to esatblish his case before professionals in the field, not before the general public. There are dozens of pseudo-scientifc books out there that are full of trash but which make their authors tons of money because of the gullibility of people. In fact it would be very easy for a scientist who had the mind to do it, to intentionally write a book like Cremo's. Now, I'm not suggesting that he doesn't believe what he writes, but his argument for why he cannot get his ideas acepted is the same argument as used by proponents of perpetual motion - namely, the establishment refuses to listen to me.
So how do we proceed? There simply isn't time to examine every harebrained idea. If Cremo's case is important for Creationists then they should spend the time and effort looking into his claims, and do so objectively and dispassionately rather than merely accepting them because they happen to coincide in some aspects with their beliefs.
There is ample evidence, on the other hand, at the DNA level that evolutionary theory has predictive power - we can predict that an unknown organism will have at least some genes that are similar to humans. The frequency and distributions of these patterns allows phylogenetic trees to be constructed which accord extermely well with observations. So, until something better comes along it makes no sense to abandon a theory with predictive capacity for a set of ideas that cannot, apparently, be defended in scientific circles.
Gedanken