2H4 nailed it as to what the big deal is. What he describes happening is every pilot's fear. We do not need to worry about how our actions or reactions will be percieved in hindsight during an emergency. Pilots are already subject to background checks, medical checks, proficiency checks, line checks, and regular harrasment by the TSA
. We do not want to be watched every single second we work. The flight deck should be a place where all that fades away and you can concentrate on the work at hand. It should not be a place where you have to worry about who else is checking up on you. Many would argue that if you don't do anything wrong, then you have nothing to fear. I disagree. That excuse has been used for various encroachments into personal lives. It doesn't make it valid.
Furthermore, FDR's are already abused by companies and I can only imagine what abuse we would see from video. A modern, digital FDR can provide all the data needed to reconstruct an accident to the nth degree. At some point it comes down to trust. You have to trust the people you give the responsibility of operating the aircraft. If you don't, why were they hired in the first place?