The problem is some idiots think their theories are facts rather than theories. Unchallenged belief is usually a fatal condition however. The larger and more complex the activity the greater is the need for theory. If we want to do absolutely nothing, and just lay back and vegetate of course we don't need theories. But any successful action needs good theory to make it possible.
Theory is power.
There could be attempted objections to this, a mystic might say they are following their own inner light. Similarly a naive Marxist might believe that in working with the 'historical process' theories generate themselves as we encounter new practical problems. Other people have said that they have no rational goal and act purely according to their feelings, achieving things 'naturally'. But these are all still theories and govern how they act. One fundamental thing they have in common is the ancient theory of an ordered cosmos.