This is a two fold issue.
First, effectively conveying ideas. The most effective way to understand others and be understood is not necessarily being either as literal or as socially unfiltered as possible, the "civilized" speech protocol was created to allow for both parties to minimize the emotional reaction during the conversation, not necessarily to hide the truth. Arguably, this manner of conversation is less of a psychological mind game than so called "unmasked" speaking.

Two, being honest about what you want and if it is possible precludes unfiltered/"honest" conversation.
You know the other person would hate you if you acted as carelessly and antagonistically as you really feel and the other person knows it too, but you agreed to not do it because you WANT to avoid fighting with that person.
This is not masking or a communication barrier, this is just a simple barter.