This seems to be the case, unfortunately. As it also seems to be the case when it comes to "beliefs" in general. But I digress.
Some proponents (with or without scientific training) have their judgements similarly impaired by emotional attachment, arrogance, ignorance (unwilling or not), stubbornness, profit, etc. Of course, they say the same about skeptics.
Aniway, I think people do have to right to belive bigfeet are real and wander across most of North America. But its also my opinion that no one has the right to say the currently available evidence is enough to back such claim. They must acknoweledge the many weaknesses present at the available pieces of evidence and reasonings. Hiding such flaws under a carpet sewed with wild baseless speculations will not strenghten any arguments and evidences. Attacking skeptics for not being convinced by flawed arguments and evidences will also be of no help. Such tactics can only create an illusion of relief or safety on the proponent, but the arguments and evidences will continue to be flawed. And the reputations of the proponents, as well as their causes will be damaged.
Getting rid of these flawed arguments and pieces of evidence (or at least use them with the propper caution) will be very good for their cause, even if they become almost empty-handed. The "default position" of a proponent, in this case, at least for now, should be something like "I believe they are real, but I am not aware of any reliable evidence at this moment to back this claim. The pieces of evidence may be enough to convince me and some others for one reason or another, but their quality is not good enough for scientific purposes, for example." This should be valid even for those who claim to have actually seen those beasts.
This would spare a lot of time and bandwidth, besides contributing a lot for a civil debate. I acknoweledge, however, that probably it would not be so fun...
Sorry for the long rant... Not the first time I rant about this aniway...