I’m not sure that’s what is implied; it’s just obvious that publicly proving one’s “true motives” is quite difficult.
When someone argues for ubiquitous mass surveillance, ask them to explain exactly how the Stasi worked, how they came to power and what can be done to keep it from ever happening again. Point out that these questions have to be addressed before arming the state with surveillance tools that previous abusive regimes couldn't have dreamed of.
You have world history littered with examples of mass surveillance platforms being used for oppression.
No explanation or justification of why that happens seems necessary! It's a stronger and supported argument to just say "Whatever the cause, when mass surveillance has been implemented historically, it is eventually used to errode civil liberties and increase population control."
These people have obviously never tried to get four people to agree on what movie to see.