I'm not sure exactly how to "feel" about Sasquatch or similar, but Hamlet put it best: "And therefore as a stranger give it welcome.There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy."
Here's Jane Goodall on the issue, always interesting to hear her speak:
The absence of evidence, not the evidence of absence, and all that.
I know, really an "academic" answer where I'm not marrying either side, but it's an interesting discussion nonetheless.
More personally I guess you could say that, knowing how often the fossil record gets re-written (it's not an every day thing, but it certainly isn't "set in stone" if you'll excuse the pun), and that there are plenty of other hominids that shouldn't exist (but did), it's not beyond the realm of plausibility. The real question is, should this creature (or some other hominid) exist, and we can somehow demonstrate and document this, then what do we do? What if they're intelligent life? (I hate this phrase, but I think most people know what I mean by it) Do we exterminate them? Or try to integrate them into your society? etc.
And I think that's really a big unknown for the most part. We can deal with animals like dogs or cows that are fairly easily to claim dominion over (be it religious, authoritarian, whatever), but how do you deal with sentient/sapient life as the "other?"