In my opinion, one of the dumbest and most illogical expressions ever is the one that goes: "50,000 [insert whatever] can't be wrong!"
This expression is routinely used to justify large groups of people jumping on some particular bandwagon. Like, "50,000 life coaches can't be wrong!" Or "50,000 Atkins dieters can't be wrong!" Or "50,000 women who like "Fifty Shades of Grey" can't be wrong. Or whatever.
It doesn't HAVE to be 50,000, of course. The point is that generally speaking, a large number of people holding a particular and uniform set of preferences, beliefs and/or ideologies is usually evidence of the exact opposite of this aphorism. In fact, the more people that are out there thinking the same exact thing without questioning it, the worse the situation usually is. Look no further than Nazi Germany or North Korea, for example.
When it comes right down to it, millions of people can--and often are--very, very wrong. 50,000 whatevers can very, very easily be very, very wrong.
The only related expression I have ever heard that is stupider and more illogical than this was for a late night TV snake oil supplement called "Focus Factor," which was supposed to allegedly improve concentration and make you smarter.
They were giving away free samples, and the woman in the ad literally said (and I shit you not): "They're giving it away for free? It must be good!"
Now THAT'S a person who could use some smart pills.