I shared an office with a PR firm for many years and I'm friends with several PR professionals so I know the gig fairly well.
I would say most folks don't really have a clue about what PR firms actually do and if they did their opinion of the profession would probably go even lower

Protecting an image or spinning a message is what most people think of but that's only the most basic form of PR and not the bulk of what they do.
Go pick up a magazine...most any magazine...find an article about a place, a resort, a chef, a book, damn near anything and I can 100% guarantee you that piece was actively promoted or even partially written by a PR firm.
Most travel and food magazines are basically giant advertisements no matter how genuine an article may read, if it contains positive information about a company or a product, it was placed there by a PR firm.
The same thing rings true for TV. If you're watching the travel channel and they have a show about the 10 best places to ride a lama, you can bet money the #1 if not the top 5 places were "suggested" by their respective PR firms.
This is the bulk of what PR firms do. Call up media outlets and suggest stories about how awesome their clients are.
The media in turn gets a no-brainer story handed to them on a platter which they'll bite on 90% of the time.