Oh, Sweaty, at last you noticed it! Why it took you so long? And I'm happy to see you like it and seem to agree with it. Now, shall we see how Russell's quote apply to bigfootery?
First, the big picture. Here's Russel's original statement:
It is undesirable to believe a proposal when there is no good grounds whatever for supposing it true.
Good grounds would be reliable pieces of evidence and/or proof. Got some? No. Then we must say...
It is undesirable to believe bigfeet are real when there is no good grounds whatever for supposing it is true.(*)
Now, let's check the issue you seem to hope that will draw people's attention from the real issue, the big picture, the bigbearfoot (**)...
It seems you are failing to acknoweledge that what's actually at stake is the very quality of the evidence you folks show us. What are you presenting to back your claim that bigfeet must be primates? Unreliable evidences (eyewitenesses reports and a film highly suspected of being a fraud). No "good grounds" here, Sweaty. Show us how you can fully discount the possibility that these animals -if real- are a product of evolutionary convergence. The propper classification of a species requires a specimen and/or DNA. Got some? Actually, since presently there is not a single piece of good evidence to back bigfeet as real creatures, we will be back to...
"It is undesirable to believe bigfeet are real when there is no good grounds whatever for supposing it is true."(*)
You are sailing (better say sinking) in the same boat where Historian, Beckjord, Mary Gree, the pigfoot guy and Tianca (as well as many others) are. Some bigfoot myth versions are wilder than others, but the bottomline is that there are no reliable pieces of evidence to back any of them, regardless if you are defending earthly flesh-and-blood primates unknown to science or aliens who abduct human females for reproduction.
(*)Yes, you may entertain the though or the hope of them being real.
(**) Here are some of those issues again, your evasions and diversions won't make them go away (at least not here):
-First of all, there are no reliable pieces of evidences presently available which could be used to back the claim "bigfeet are real" and the methodology and reasonings used by footers to support their claims quite often have big flaws and gapping holes. All other issues pale when faced with this one.
-The absence of a known chain of custody and the fact that the originals are not available for examinations render PGF (taken by many footers as the pièce de résistance when it comes o bigfoot evidence) an unreliable piece of evidence.