People are always communicating passively. A communications expert, which I am not, will tell you that less than 20% of communication is the words from the mouth even in a face to face oral conversation. Think of communication in 3 layers:

* the words

* the voice

* body language

Truth only occurs when those three layers are in agreement. This means people are frequently untruthful and generally unaware of just how obvious their lack of candor is to somebody who listens well. Since you are usually not in full cognitive control over your voice and body language, and sometimes even over your words, most of your communication will be passive regardless of your intentions and level of control. It takes a higher state of awareness to be a good liar and that can really age a person.

Well, you're not really defining what you consider 'passive communication' or why you harbor this view, so there seems to be material missing to formulate a nuanced reply.

Assuming you are defining "passive communication" the way the parent comment does, the answer seems clear: passive communication does not engage, examine or disclose its beliefs, but instead papers over their existence and applies them indiscriminately. The passivity of that communication is rooted in tone, but not about conflict avoidance or politeness as the examples listed under active communication suggest - rather, it's a tone of wheedling insistence, if such a racy and vivid metaphor can be accurate.