Why would anyone use machine learning if not to create systems they don't understand ? That's the whole point of doing it. Not having to understand complex system to understand -or even predict- them is a very good thing indeed. I don't know anything about how to mathematically analyze pixel values to read text, but I can create such a formula using machine learning. After creating the formula I know nothing more about it. So the same person can create programs to read text, transcribe audio, predict loan repayment, ...

And when it comes to the bias in the data - bias in the system thing, well, same thing goes for human judgement. Another way of putting this would be garbage in-garbage out. Humans might be able to tell you of bias in the inputs, rather than just using it, but this ability rapidly deteriorates when the dimensionality of the inputs rises. You can tell if there's something weird about combinations of 3 numbers, but you can't tell if there is something off about 150 number sequences.