antidepressants have been tested against placebos, and have consistently preformed better. it's scientific fact. i'm sorry that your sociology teacher is full of crapy
antidepressants do not, however, work for everyone, and antidepressants alone usually do not work as well as psychotherapy, alone or in combination with meds.
but psychiatrists believing they work and continuing to prescribe them definitely doesn't prove they work! there are a really disturbing number of people out there who continue to administer treatments that are actually shown to cause harm, let alone ones that just aren't proven to work.