The dominant public perception of physics is that it is tedious, abstract, and fundamentally irrelevant; the challenge in an introductory course is to convince the audience that physics is rewarding, fun, useful, and most of all a worthwhile endeavor.
Even at research universities, teaching is now playing a larger role in promotions and tenure decisions. In this brave new world, a physics graduate student who aspires to an academic career dare not neglect the teaching side of her or his graduate training.
Unfortunately, physics discussion sections very often fail to live up to this intent. Too many students come to discussion sections with the intent that they will get their weekly homework "done for them" by the TA.
Unfortunately, research carried out by physicists has shown these "common sense" ideas are in the main incompatible with correct physics. Worse still, these erroneous ideas are robust and difficult to dislodge from students' minds, in large measure because these ideas are not addressed by conventional physics instruction.