I do not think that anyone can be completely objective or subjective in the learning process. When observing an event and communicating it to others, the observer has to start the observation from his or her own standpoint. The subjectivism is reduced, however, when the observer starts to communicate and share understanding with others who do not necessarily have the same ideas. This claim precludes any possibility of, or the need for, communication. There would be no society if there were no need for people to negotiate or share a reality.
Many constructivist theories are inappropriate for entry-level learning.
At entry-level students do not have the preparation for decision making on what and how they should learn. The educational goals, objectives, contents, and even learning methods have to be decided under close supervision of the teachers. Concrete teaching is necessary before students attain basic knowledge and skills to make free exploration. The teacher's control may be gradually reduced at higher grade levels. It is unnecessary for students to look for a way to prove why the sum of the three interior angles of a triangle must be 180 degrees but not anything else.