As everyone else responded - do not be led astray by this event. Even consummate professionals encounter boorish audience behavior. I don't believe it is wise to use the student body as a captive (forced to attend) audience, for it only encourages the kind of actions you witnessed. Like any other "assembly", there are many in attendance who object to being there. Your school should schedule concerts for parents, other schools (elementary, middle, other districts) and the community. You would not experience the same attitudes in those.
Please don't give up your dream. Music is a wonderful gift and getting to teach it is an even greater gift. For many of us, music in all its forms - performing, listening, composing, teaching, is the most important thing in our lives. In times of darkness, music brings light. When you are afraid, music brings you courage. When you are lonely, music brings companionship. When you are ill, music heals. Music will bring you sanity when all around you there is craziness. Music is a divine force that can propel you through all phases of life.
So ignore the boors and go for it! You will not regret it.