Below is the frequently asked question that I encounter in my Free Software Philosophy sessions.
"Surveillance is impossible with free software, that’s correct. But that doesn’t mean surveillance is always possible with proprietary software.
For example, Microsoft office might be spying on what we write in documents. So we can have a trustworthy government organization that can check code of MS office application privately and rate the security of the application. Let the users decide whether to use it or not use it. If not one organization, we can allow multiple organizations to review privacy and security of proprietary application by inspecting the code.
This way we can cross-check availability of any backdoors and also keep the application still proprietary to safeguard their business concerns."