They are accusing Moses of appointing himself. "You take too much upon yourself. We're just as good as you." Yet, that is not the issue. The issue is respect for God through the office He had appointed the man to.
It is easy to feel put upon by government—municipal government, state government, national government—governments in general. They take advantage of us. They put the pressure on us through taxes. They won't allow us to do things that we feel we ought to be able to do. We can begin to feel as though we are being taken advantage of by government.