This is about cameras in secure facilites, such as in a prison or jail. Those spaces should be subject to some form of public inspection but there's probably a good argument to not allow random cameras in.
Earlier this year various elected officials tried to perform exactly that kind of public inspection of ICE facilities and met a lot of resistance. I know that some subset of these were just publicity stunts, but despite that, the fact remains that the public needs to be aware of what detention in those facilities is like and if the DHS makes choices that result in random cameras being the only way to do that, then they should reap what they sow.
you're right. there's also an awful lot of very obvious good arguments for allowing recording and public access to recording, such as the incident where a prisoner was locked in a scalding shower until he was so badly burned that his skin "fell off at the touch" (https://en.wikipedia.org/wiki/Killing_of_Darren_Rainey). Like so many incidents of its kind, there was absolutely no hard evidence available to prove what happened and it ended up being yet another case where someone died horrifically and officially no one was found to have done anything wrong but several million dollars did change hands. If prison guards are torturing prisoners to death and getting away with it, the argument that they don't need surveillance needs to be a whole lot better than "probably good".
About as good of an argument as the prisoner who insists that cell searches for contraband must be announced a day before the search. Do you think the people running the jail would go for that?