The monsters won't come in the form of zombies or vampires, rather they will resemble those that are the most trusted in society, that of public servants and representatives of the people or a higher power. Their persuasion will be so powerful that those that aren't constantly critical of authority would be swept away with the current of support by the incompetent hoards.

The support of the masses makes it extremely tempting for other, non-incompetents, to join the crowd in hopes of exploiting the trust for gain, for nothing is more lucrative of a venture than taking advantage of the gullible. I used to think that nobody desired being ignorant or stubbornly wrong, however, most don't know of their ignorance and the wrong don't believe the right due to barriers to accurate information or the abundance of faulty information.