Polarising topic. Many more parents than people realise do use sedatives. Some are using them in certain medicines without even realising it. Lots of parents swear by using antihistamines to induce sleep. I mean countless parents use sedatives on planes for instance.
Personally speaking I would never ever use these. I think its dangerous and unnecessary. However the law is pretty loose around it. So to be honest its a bit of a moot point as they've done little wrong.
As for taking their kids or some middle class privilege. I have seen first hand people akin to your Mick and Sandra, neglect their kids in far worse ways over a long period of time, and still not have their kids taken away. The law has simply acted as normal.
But the parents sedating their kids all across the world, or those neglecting them in far worse ways, aren't at the centre of a high profile media obsessed case so they get judged by different standards. At least by the general public anyway.