One person asked me about this by e-mail. To clarify, my last entry was indeed about "affective communication", i.e. the communication of feelings, not about "effective communication", i.e. communication that is successful in conveying the intended message. Anywhere where I meant the latter, I used that terminology, but my main interest was the former.
A great deal of our communication of emotion is not even conscious. However, we continually give off powerful signals of our feelings, e.g. by way of facial expressions. Contrary to what was once thought, the "language" by which we do this is strongly cross-cultural. Moreover, we are very good at "reading" other people's feelings and we are highly responsive to them. My suggestion is that this kind of communication and responsiveness provides a large part of the glue that enables human beings to bond into societies, and to show some sympathy for others who are not actually part of their society. (Hence, there is no social contract in any narrow sense, just a complex set of factors that glue people into societies and into a larger moral community.) There is a problem whenever we engage in forms of communication that lack these resources.
In some cases, however, the communication of emotion may actually reduce effectiveness (e.g. I can be distracted from the consciously-intended message of someone who is sending off anger signals and so appearing to be a threat). Thus, affective communication and effective communication are definitely not the same thing, and nor is the former merely a part of the latter. The relationships between them may turn out to be quite complicated. My thesis is simply that moment-by-moment affective communication is enormously important to human beings and that any technology which reduces it thereby has a downside.
That is not to deny that such technologies may be good, all things considered. There is just so much valuable communication going on as a result of print, telephones, the internet, etc. I wouldn't be without any of this. However, there could be situations where threats to affective communication could strike at our social bonding with each other or with other intelligent beings (could, as shorthand, strike at the social contract). This seems to me to be a serious problem for many actual and postulated technologies - a much more legitimate problem than most of those that are commonly raised, and one that should be factored into discussions of the ethical development and use of emerging technologies.