I read accounts of FREIXEDO. His take on the phenomena is similar to KEEL's or VALLEE's: a manipulative intelligence deceiving us by taking on many shapes. Like SIDER, he thinks that it has vampiric attributes. He agrees with those researchers that it can sometimes be hurtful or helpful to persons it contacts, looking alternatively 'good' or 'evil'. The truth being much less simple. Interestingly, he began with a black-and-white view, but came to change his mind.
As a whole, I am dubitative of crypto-terrestrials. But I think that it covers at least three different points (I exclude time-travellers from our future, or visitors from alternate Earths, they're different matters)
-1)The idea of an hominid from the genus Homo having evolved parrallely to Homo Sapiens is interesting. If he diverged from our lineage early, he could have become a large-brained humanoid. But I think it's highly unlikely. We know a number of human fossils, none of them at any time looks like this supposed hominid. I know that we know only a limited number of archaic human remains. But this is still anomalous. He should have become the dominant species at the time he evolved, at least that's what this hypothesis says. We should find his remains first, and have much less chance to find other, rarer ancient humans. Plus there are a number of other serious problems: we know the bad side of human behaviour. What he sees that can exploit, he exploits. A dominant Homo would have reduced other humans to slavery or driven them to extinction. If they developped an advanced civilisation, it is surprising that we find no remains at all. To develop advanced science and technology, one needs a strong social back-up, not a reduced community on a small territory. I don't believe in 'secret societies' or hyper technological Atlantis. I am ready to believe in the existence of quite advanced, pre-industrial civilizations at the end of the last Ice Age. There is evidence of them. But a society, more evolved than ours, or a more intelligent human species are very unlikely. And why would they hide at all?
-2) Relating to small big-headed humanoids, it is true that many look more or less human. Some of those apparitions are maybe not material, some holograms or projections. Or they could be robots. But it is possible that some at least are really modified humans. But they more probably wouldn't come from hidden civilzations; their existence would suppose the action of aliens, as herders and genetic manipulators.
-3)If a hidden close relative to us seems implausible, what is it of intelligent terrestrial beings evolving in a far remote past? It is difficult to conclude as abruptly. Humanity does not exsit for a long time, at a geological level. We have many difficulties to find human remains 1 000 000 or 500 000 years old. And we're greatly helped by the fact that they're recent. In 100 000 000 years, most of them will have been destroyed. If we are to become soon extinct, a future paleontologist from this time would have great difficulty to discover our existence. After all, humanity became numerous only 10 000 years ago, a blink of an eye geologically speaking. This future paleontologist would see a greater rate of extinction at this time. But as the Pleistocene was filled with a number of mass extinctions, and the end of the Tertiary before, it would be very difficult to discriminate. See the difficulties to reconstruct the exact frame of events at the end of Cretaceous, Triassic or Permian. It is likely that very few traces of the existence of humanity would remain. So we can't be sure that no sentient, technology-maker animal (and probably not humanoid) evolved in a more distant geological period. It could too have been less prone to pollute and destroy its environment or proliferate. It could have evolved space travel. It could still be on the planet, or left it but be monitoring it. And, why not, be Fort's herder and behind UFOs and a number of phenomena. This hypothesis is perhaps not as plausible as the ETH; but we can't reject it.
along with lies, mistakes, subterfuge and natural phenomena.