[olliej]

How would publishing the source help?

There are plenty of reasons that are reasonable for saying “source code should be available”, but “the software might have bugs” is not one of them.

[eesmith]

https://www.bbc.com/news/technology-17631838 gives an example of an insulin pump with a security flaw that made it possible for anyone to send a signal to dump "the entire cartridge of insulin into its host's bloodstream."

That was found by a security researcher not affiliated with the manufacturer.