Bigfoot is nonsense. Firstly, there is no contemporary evidence for it. A few pieces of shaky footage, some footprints and hair samples that don't have DNA in them or are contaminated are not evidence. Secondly, we have no evidence from the fossil record that any ape-like creatures existed in North America. We have a pretty good idea, for instance, about the pleistocene fauna, but there is no bigfoot in the La Brea tar pits, not even a monkey.
Thirdly things about it just don't make sense. Thousands of people have been looking for it in the last fifty or so years, without any success. Let's compare this with another large ape, the Bili Ape. One researcher went to the Congo in the mid-1990s to investigate native stories about a large ape that's not a chimpanzee or a gorilla. On his first trip, he found a skull and managed to buy perfect quality trail camera photos (This one:
http://img180.images...oapenormqi5.jpg compare it with the blobsquatches), take casts of footprints and collect fecal samples. He gathered more evidence in one trip that exists about bigfoot altogether. In 2000, he went back and found ground nests belonging to the animals. After the end of the civil war, yet another trip saw the animals, confirmed them to be an anomalous, isolated population of huge chimpanzees that have been studied ever since. Why was Karl Ammann successful? Because the animals he was looking for were real.
But there are other things that make no sense about bigfoot, all of which have been discussed ad nauseam on these boards. Every anima (including humans)l in the US is hit by cars from time to time, but not bigfoot. There is no sign that bigfoot eats anything, because our understanding of the ecosystem doesn't seem to have an ape-shaped gap. Most bigfoot sightings are near large population centres, which suggests that someone would have taken at least a clear photo of it. Everyone has cameras now.
And I don't really buy that cultures all over the world have such stories. There is a "hairy wild man" archetype in folklore, but its existence doesn't have to refere to anything real (animals are hairy and are wild, so a wild man would also be hairy, to distinguish it from just "man"). I also believe that bigfoot proponents consciously and unconsciously interpret all such stories as bigfoot-like, while in reality there aren't many similarities between the stories, they just project their biases onto these tales.