Okay, there's a lot of confusion out there, all because of the word "passive".
The word passive, in everyday language, may mean "not doing anything", "not reacting to stimulus", "only reacting to stimulus", "being sluggish, lazy..." and so on. Culturally, "passive" is tagged as bad, so anything which is associated with said word must be bad by definition.
Now, there's a grammatical concept called the "passive voice", and - probably because of the word "passive" in it - it has taken lots of slack from usage manuals (including Elements of Style). These usage manuals (including Elements of Style) are vague about what's supposed to be passive about the constructions and don't help you decide, really. It's almost like a religion: "passive voice" is "passive". We don't have to tell you what it means. The "active voice" moves in mysterious ways.
But the word "passive voice" is a label. What is "passive" isn't the voice, but the subject of a verb in the "passive voice". And this has a very specific meaning, too:
"She was given a present," vs. "She received a present." Grammatically, "she" is passive only in the "was given" sentence; "she" is "active" in the "received" sentence. Semantically, the real action is done by someone else in both sentences. The sentences refer to the same person in the same context. There is debate about whether using "received" makes her seem more active, because of the way grammar frames the situation.
There is, however, another - unrelated - school of thinking about words, that occasionally uses the word "passive". These are words that "do nothing to invoke a vivid meaning". The theory is that there is a hierarchy of concepts.
1. The more specific the word, the more work it does (and the less it leaves to the reader): for example, "hound" is more active than "dog".
2. Function words (words that express grammatical relationships) do not invoke meaning and are therefore "passive" in that sense, that their "evocatively neutral". This includes helping verbs as well as articles, conjunctions, etc. The idea isn't to get rid of them, but to reduce the ratio in favour of "evocative words" ("active words").
Now, since "to be" is a helping verb, it increases the "passivity" of a text (in the above sense), but it can also collaborate with a main verb to create the "passive voice" (another use of the word "passive"), which is considered "passive" (again, another use of the word "passive"). This is a terrible muddle, and it doesn't help that not all people agree with either of the stylistic concepts.