Not everyone believes this. There are a number of dumb and useless features about the human body.
People choke to death because both breath and food go down the same pipe.
The conventional explanation for all this, and the appendix, is that evolution proceeds by jury-rigging previous designs. The plan of this creature was adapted slightly to make a new creature, and so on until you get us. Argonne National Laboratory, Division of Educational Programs, Harold Myron, Ph.D., Division Director.