They discourage bad habits when driving.
It doesn't matter if you like them or not ( I don't )
Yes , cameras and the videos that they collect can be misused. Yes , it seems unfair to have a camera watching you all the time working. And yes , there needs to be federal laws allowing people some type of ownership of the data collected and it's potential manipulation.
Even with all that said , a camera hanging over your head is , at the very least , a reminder that if something stupid happens , it will be preserved forever so you may want to try an avoid that.
I want to be TOTALLY against cameras but , I can't because of what I see everyday when I drive. People in big trucks , head down texting. I will lay on the airhorn and they won't look up.
Honestly , if I started a trucking company right now , I would have cameras dangling all over the inside and outside of the tractors ( except for the sleeper )