Is there a word for something loved by the masses but whose true value is lacking?

Solution 1:

"Snake oil (wiki)" seems to fit the bill.

Solution 2:

Calling it an "old wives' tale" would work. From Merriam-Webster:

old wives' tale (noun)

a common belief about something that is not based on facts and that is usually false

Solution 3:

You can consider nostrum. It is a medicine in conventional use but not proven to be effective, or an ineffective but favorite remedy, scheme, theory etc. to solve a problem. It comes from the Latin phrase nostrum remedium "our remedy".

OED definitions:

• A quack remedy or patent medicine, esp. one prepared by the person recommending it. Also in extended use.

• fig. A means or device for accomplishing something; a pet scheme or favourite remedy, esp. for bringing about some social or political reform or improvement.

Solution 4:

The word "fad" is not always pejorative, but if you use it to describe something that others take seriously, then it comes off as insulting.