If there is a "very convincing philosophical argument" that we should go with the majority, and yet we see the majority holding countless silly beliefs that even a little bit of primary evidence and some cursory examination show as being invalid, what does that tell us?

It tells us that the very convincing argument has at least one fatal error. It tells us that our ability to be convinced is falliable. And it tells us that our argumental-validity-checking has some bugs.