I think it's ok to expect that 'locked' means locked and that restricting access to phone functionality in a 'locked' state be something that is available to include access to the camera.
I have kids and also work in an environment where people do 'silly' things. If my kids grab my phone and take a bunch of photos that I discover later (which has happened) it's not a parenting issues, its kids being kids. If my co-workers decide to grab my phone off my desk as it is charging and take silly photos (which has happened) it's not a work environment issue, it's co-workers being co-workers.
With my MacBook, locked is locked and when it's out of my line of sight, I know it's truly locked. With the iPhone the functional ability is there to disable the camera, but the option is not available as a tradeoff for convenient camera access...as most ppl use their phones as their main camera source nowadays.
If the answer is that Apple does not allow the camera to be disable on the lock screen without disabling the camera feature, then that's the answer...but there is no need to invalidate the concerns of others.