This isn't "Government" monitoring (even if a government agency is watching their own in acting as a form of commerce, ie: a government operated railroad). Having a job and being expected to follow rules is hardly an issue of individual "Liberty".
As for John Locke's Social Contract theory, again, we're not talking about government infringing on personal liberties. We're talking about the safe operation of a mode of transit where there is a significant amount of human lives under the control of a single person.
Aircraft MUST be operated with a crew of two in the cockpit when acting as an air transport. That's the FAA rule. Manufactures also have rules that say you gotta have two in the cockpit. There are only a smattering of jet aircraft that don't require a crew of two, and only when flown for non-air transport purposes.
Taxi and bus drivers can be seen by the passengers. If something is wrong, they can in effect mutiny. They don't have that luxury on a train like Metrolink.
I remember as a kid in Japan, the cab of the EMUs had a window behind the driver. They had the luxury of choosing whether they wanted to close the curtain or not. Loved it when they didn't. Without ANY exception and over hundreds of rides, I've never seen a Japanese commuter train driver act unprofessionally. Some actually called out every signal, every light, every indicator on their panel audibly - not for an audience, but because it was their job. They wouldn't care if there was a camera or a supervisor in the cab - they were doing their job.
Now, I haven't been there since texting came into existence, but I don't suppose things have changed at all.
Back to Dutchrailnut: Dude, you don't read, do you? The comment was specifically referring to the fact that they won't catch an infringement with the cameras immediately, but if they review the material on the hard drive regularly without prejudice, the could observe trends.
As for Metrolink, if they have disciplined Sanchez and he kept breaking the rules, the blood of 25 is on management's hands. Make cab distractions an immediate terminable event. Goes for freight operators that share their own lines with passsengers, too (ie: Amtrak).