Heartbleed and ShellShock are examples of why open source is better. Both were found by folks who were not the software maintainers, but were reviewing the source code independently.
In comparison, it took multiple deaths and a major lawsuit to create the same level of visibility into Toyota's codebase. And what reviewers found was code quality far worse than that of OpenSSL or bash.
Someone else said this in another HN thread, but I love it: imagine a world in which Consumer Reports car reviews include a code audit report. That would be far, far better for overall safety than the current situation.