I find people who agree with me for the wrong reasons to be more problematic than people who simply disagree with me. After writing a lot about why free software is important, I needed to clarify that there are good and bad reasons for supporting it.
You can audit the security of proprietary software quite thoroughly; source code isn’t a necessary or sufficient precondition for a particular software implementation to be considered secure.
You make a lot of good points here, many of which I actually agree with.
The article focused on studying the behavior and properties of software. For completeness, it mentioned how patching can be crowdsourced with the example of Calibre. I also described how FLOSS decreases dependence on a vendor, and wrote two prior posts about this linked at the top.
I never claimed that source code is useless, only that we shouldn’t assume the worst if it isn’t provided.