Firstly I don't think 'mandatory screening' means you have to consent to it. After dd was born, our military pediatric clinic implemented this type of general depression screen for new moms. But there was no penalty for refusing it. I think the 'mandatory' part comes from hospitals or health professionals being forced to offer it to all clients.
I have mixed feelings on this type of general screening. I can see the point of it - early intervention is a good idea. I'm sure my mother was depressed a lot of the time and I wish someone had tested her, and intervened in my childhood a bit!! I had a teenage brother who also committed suicide. My mother wasn't in any position to help prevent that and probably contributed to it. This kind of general screening may have helped in our family.
However I see huge potential for misuse. I actually was clinically depressed during my pregnancy and was having treatment (first meds then therapy). However I didn't have any PPD. In fact I stopped going to the weekly therapy sessions after dd was born because I was too sick physically and couldn't get there. That was my choice and my assessment to stop treatment and my psych. was fine with that. However I later answered the Pediatric clinics screening questionnaire and scored in the depressed zone (although I wasn't clinically depressed at this point according to both me and psychiatrist). And after a ped visit when I stormed out cause they wanted to vax my 2mo old WITHOUT her even seeing a doctor first, they wrote something like "mother angry and refusing to vax, scored high on depression scale, further evaluation warranted". That really made me angry and I changed hospitals. As a former CPS worker, I can see how this info could be misused by general health workers. I doubt psychiatrists and mental health workers would misuse it.
One thing to note is it is ONLY a SCREENING TOOL. It is not a diagnosis. However I can see general health workers using it as a diagnosis. I think it would be totally inappropriate for this information to be conveyed to CPS for example. It's simply not accurate enough. It's like trying to use that blood test, AFP? to diagnose Downs Syndrome.