Trust.
Open software has given us trust.
I do not trust Apple. I do not trust Microsoft, or Oracle, or IBM, or Novell, or Sun, or SGI, or SCO, or Compaq, or Wally der Wanker down the block -- any number of closed software developers on whatever scale.
I trust the source. I trust in a culture where development of the software involves open discussion of the flaws and failures of the source, where changes to the source are public, where features are weighed and demonstrated before being merged into the main codestream -- where software must have been written before it can be deployed. I trust in an infectious license that explicitly prevents the source from becoming closed.
I cannot build my future on the foul vapor of broken promises and misplaced trust.