Motivational Posters Of Green Acres, Part IV

A sign on the wall of a Green Acres hallway reads:

PEOPLE WITH MENTAL ILLNESS “CAN CONTRIBUTE SO MUCH TO THE WORKFORCE AND THE WORLD IF GIVEN A CHANCE”

Although I entirely agree with the statement, I am confused by its presentation. What do the quotation marks mean? If this is a quotation, who said it? And did he or she say only the part about contributing, not the part about mental illness? If so, who added the mental illness preamble?

Or, are the quotation marks meant to indicate that this is a “dubious” or “so-called” sort of “fact”, that is not really “true” per se?

As with so many of the mysteries of Green Acres, we “shall probably never know the meaning."