From Geoffrey K. Pullum, the sassiest abstract in the history of academic writing:

Writing advisers have been condemning the English passive since the early 20th century. I provide an informal but comprehensive syntactic description of passive clauses in English, and then exhibit numerous published examples of incompetent criticism in which critics reveal that they cannot tell passives from actives. Some seem to confuse the grammatical concept with a rhetorical one involving inadequate attribution of agency or responsibility, but not all examples are thus explained. The specific stylistic charges leveled against the passive are entirely baseless. The evidence demonstrates an extraordinary level of grammatical ignorance among educated English language critics.