A consensus of experts, even a majority consensus,) is certainly a legitimate piece of evidence to consider in building a case to accept or reject a proposition. But there is a fine line (and sometimes a rather thick, albeit obscured one) between using this piece of evidence competently on the one hand and deceptively on the other.
For starters:
1) A consensus of experts (COE) should be regarding a subject that is subject to expertise. Meaning, it’s the kind of thing we have lots of experience with. That is, after all, how expertise is established.
Even when criteria 1 is met…
2) COE ought to considered only if the experts have expertise (lots of experience) in the subject they are offering an opinion on
Even if criteria 2 is met…
3) We should remember that COE is one type of evidence. We ought to consider the weight of contrary evidence. If there is sufficient contrary evidence we ought to leave the matter unresolved.