Earlier quoted context omitted.
It's unnecessary. If you want to prevent something from being patented, just disclose it in a publication. That publication will bar anyone else from patenting your invention. As long as you don't patent it yourself, it will become dedicated to the public.
Not true anymore, unless that publication reaches the vast majority of practioners so that it has clearly become part of the normal state of the art (recent court decision) - something very difficult for a private citizen to accomplish. Mere publication to establish priority doesn't matter because priority doesn't matter, being first to the patent office matters; so big companies can legally steal your ideas now. Eve…
First-to-file resolves priority when it comes to undisclosed inventions. Two inventors A and B both invent some new invention and both go to patent it. Whoever is first wins. Two inventors come up with the same invention all the time. The first-to-file rule makes it easier to resolve conflicts than examining evidence of who invented first, and it encourages speedy filing by preventing an inventor from secretly exploiting an invention and then filing when another inventor appears.
By the way, anyone can look at the published patent applications (which are published usually 18 months after filing) and can submit information that they believe would be relevant to the examiner in determining if the invention is patentable. It's called a Pre-issuance Submission. [0]
[0] http://www.klemchuk.com/339-preissuance-patent-submissions-a....