am, are, is, was, and were: bad words or not?

Recently a writing friend was told to eliminate from her writing as many state of being verbs as she could, i.e. "am, are, is, was, and were." I believe the state of being verbs problem isn't as serious as some writing advisers make it out to be. It's kind of a hobby horse, often ridden by [sorry] those whose grasp of grammar is shaky. For example, they don't completely understand passive tense. They think a statement like "he was drying the dishes when the ceiling fell" contains a passive verb, i.e. "was drying." It doesn't. "Was drying" is a present progressive verb and there's nothing wrong with using it. In fact, not using present progressive verbs can lead to confusion. For example, if you say "he dried the dishes when the ceiling fell," we don't know what you mean. Like he'd finished drying before the ceiling fell or what? Passive is something else. You're using passive when the object of the action is the subject of your sentence, e.g. "the dishes were dried by him" instead of "he dried the dishes" (active). A burning question: Where is this dish-drying guy when we need him?