Basically MA works because a lot of traders use them. It's self-fulfilling.
But I believe we should be cautious when using them, and use them in the right way. For instance, when prices go through an MA, for instance, the 100 SMA, and you already have a long bias, that should give you more confidence. But you shouldn't try to gamble on whether an MA would reject prices or not. No matter what you do with MA, you have to have a bias first, and then use the MA to justify your bias.
But I believe we should be cautious when using them, and use them in the right way. For instance, when prices go through an MA, for instance, the 100 SMA, and you already have a long bias, that should give you more confidence. But you shouldn't try to gamble on whether an MA would reject prices or not. No matter what you do with MA, you have to have a bias first, and then use the MA to justify your bias.