Never say never even if its probably not in the cards. The lack of evidence doesn't destroy the possibility of bigfoot it just reduces the likelihood. Finding large new species is not unheard of. Rhinopithecus strykeri, Pecari maximus, and Rhinopithecus strykeri are a few good examples. Thats why I keep an open mind even if that is "stupid".
So we should all believe in the Tooth Fairy, Santa Claus, unicorns, pegasi, manbearpigs, leprechauns, boogiemen, and giant man-eating squirrels? There is about the same amount of evidence for each of these creatures as there is for bigfoot (i.e. none).