[0] https://www.amazon.com/gp/help/customer/display.html/?nodeId...
Parts of China is pure filth. There is no quality control until bad PR surfaces. Then it's all about saving face.
So it wasn't a case of adding deadly poison, it was a case of adding an almost safe ingredient because the manufacturers needed to get their cost down to compete. Amazingly, it appears that melamine was even too expensive and they bought scrap melamine from the manufacturing process which was not pure enough to be used in plastics, beacuase it contained the actual kidney damaging chemical rather than just the precursor.
Lots of detail in the Wikipedia article: https://en.wikipedia.org/wiki/2008_Chinese_milk_scandal
Just because only six babies died from acute kidney damage (according to the article you linked, which does not quite agree with your numbers) does not mean that's where the damage ends. Evidently there were 54,000 babies who were impacted severely enough to be hospitalized -- that's 18%, a far cry from 0.001%, and most definitely not an indication that an ingredient is "almost safe". Ignoring 53,997 of them makes your analogy incomplete to the point of being specious.