But transparency is a prerequisite for security. Free software isn't necessarily secure, but only if its free software can we check and verify or fix it and distribute modified versions.
That was true when the incentive was for vulnerabilities to be disclosed and fixed for the good of all, but sadly today, vulnerabilities are extremely valuable and so the incentive is for them to be sold to the powerful.
I think it is tremendously difficult for the layman to understand that obscurity is not security. In fact it's counter-intuitive at first.