It seemed to be a common thread among the founders that the unencumbered sharing of discoveries was a greater good. Patents serve as roadblocks creating a temporary dead end in the process of discovery. It's better to share and have everyone benefit from the fruits of innovation. Of course, most the founders were well off anyhow and patent trolls didn't exist yet, so the topic was a different matter at the time.

http://movingtofreedom.org/2006/08/31/ben-franklin-on-patent...