Public order is necessary because without it we would not be able to live our lives and enjoy the rights that we deserve to have.
Political philosophers like John Locke pioneered the idea of the social contract. They said that people have rights that they deserve simply because of the fact that they are human. They said that people get together and form societies so that these rights will be protected. This, to them, is the only reason to have societies and governments.
If we do not have public order, our rights are not protected as well as they should be. Without public order, we have much more crime than we do now. When there is unjudicated crime, we are no longer able to feel that our life and our property are protected. We do not feel as if we have as much liberty because we do not feel safe and comfortable when we are out in public.
For these reasons, public order is very important. It is necessary in order to allow us the rights that we deserve to enjoy.