I am an abigfootist, a non-believer in the existence of Bigfoot (aka Sasquatch).
I do not belong to any organization of people who do not believe Bigfoot exists (nor to my knowledge is there such an organization). I do not get together with other non-believers in Bigfoot. I do not go from door to door with pamphlets to convince people Bigfoot does not exist. I do not raise money for, or give money to, the abigfootist cause because there is no such cause.
I do not believe there is sufficient evidence to credit the claims of those who say Bigfoot exists. Therefore I do not believe it exists. My mind is still open to accept new evidence. But an open mind is not an open sewer. The evidence needs to be something better than a grainy film that could quite easily be a hoax, for example.
Of course I cannot prove that Bigfoot does NOT exist. One cannot prove nonexistence, except in very limited spatial circumstances, such as proving that there is no mouse in my teacup. You and I can both see the whole of the inside of my teacup and agree on whether or not there is a mouse there.
But to prove that Bigfoot does NOT exist would require me to show you every square foot of western North America at once.
Luckily, it is not up to me to prove Bigfoot does not exist. It is up to those who say it exists to prove it. Apparently, after decades of Bigfoot “sightings” and innumerable books and articles alleging Bigfoot’s existence, nobody has produced anything remotely like strong or conclusive evidence.
So I can never prove that Bigfoot does not exist, and the believers in Bigfoot have so far failed to discharge their burden of proof that he DOES exist by producing the necessary evidence.
Does that mean that the chances of Bigfoot existing are 50%? Not at all! Because there is also the concept of probability to take into account.
For example, you say people all over the world have stories of big, elusive hairy wild men in the woods? More’s the reason to wonder why nobody has produced a skeleton or captured one. We have skeletons and fossils of dinosaurs no bigger than a chicken who lived millions of years ago, but there is not a single fossil or skeleton of Bigfoots who live among us right now?
I am perfectly willing to live and let live, and to allow believers in Bigfoot to hold their beliefs. If other people want to believe something with no real evidence, it is neither my right nor my desire to stop them. I will even look over their books and articles to see if any REAL evidence exists.
I respect and defend the right of Bigfootists to buy media space and airtime and preach to others that Bigfoot exists. If they want to say that believing in Bigfoot despite the lack of evidence is a virtue called faith, I will just smile and sigh.
I will respect their RIGHT to hold their beliefs. But I will NOT respect their belief, because the belief in such an improbable and unproven creature is illogical and bespeaks an inability to think logically. Such a belief does not deserve respect.
I may or may not respect the individuals who believe in Bigfoot. Some may be otherwise intelligent persons who have very active imaginations and fail to understand what real evidence means. They may be very intelligent persons who were nonethless indoctrinated into Bigfoot belief in their childhood and are still too conditioned to abandon the concept. They may indeed be very respect-worthy persons in other ways.
Then again, some may be gross charlatans catering to the credulous.
Finally, if the number of Bigfoot believers should begin to grow and throw their weight around politically and socially, I will become less tolerant and I will have to respond.
Some may want to print “Bigfoot exists” on the currency. Why a piece of currency, used as a medium of exchange in commerce, should contain a totally irrelevant reference to the existence of a legendary ape-man is totally beyond me, but I am told that stranger things have appeared on the currency of at least one country. 
The Bigfootists may ask that pictures of Bigfoot be put up in public buildings at public expense. They may form organizations to lobby school boards to have them add Bigfoot to the natural science textbooks. They may ask that casts of allaged Bigfoot tracks be paid for and displayed at public ezxpense in public builings, to help others know the “truth” about Bigfoot.
They may add a line about the “mighty mountains of our land, where Bigfoot waves his mighty hand” to some patriotic songs and insist that these have to be sung by all children at school.
That is where I, as an abigfootist, start to push back.
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