You can't communicate effectively without a protocol/language/etc, but communicating is not about consensus; it's about communicating ideas/thoughts/etc. Consensus is a part of communication, not its aim.
I agree that not offending/annoying someone is beneficial and might outweigh the message you have to communicate, but that isn't relevant to discussion about the efficiency of the protocol. If in spite of brusqueness, your point comes across, then it's effective communication.
Think of the "consensus" as the embedded state within a communication.
In a feudal society a lord might send a written missive to the King or Queen, and if they did it would contain a ton of horribly polite boilerplate, because the consensus of the time on both sides was that anything less was disrespectful.
It is very possible that your lack of words in a given communication sends a point across that you never intended, even if the point you had in mind also made it across.
I agree that not offending/annoying someone is beneficial and might outweigh the message you have to communicate, but that isn't relevant to discussion about the efficiency of the protocol. If in spite of brusqueness, your point comes across, then it's effective communication.