I don't really think auditing is a compelling argument for FOSS. You can hire accredited companies to audit and statically analyse closed source code, and one could argue that marketable software legally has to meet different (and stricter) criteria due to licensing (MIT, GPL, and BSD are AS IS licenses), that FOSS do not have to meet.

The most compelling argument for FOSS (for me) is that innovation is done in the open. When innovation is done in the open, more people can be compelled to learn to code, and redundant projects can be minimised (i.e. just contribute to an existing implementation, rather than inventing a new). It simply is the most efficient way to author software.

I'm probably wearing rose tinted glasses, but the garage and bedroom-coders of the past, whom developed on completely open systems moved the whole industry forward at a completely different pace than today.