People are entitled to make mistakes, provided they are not overly detrimental to others. What is offensive is not having a mistaken opinion (particularly when this is a freshly formed mistaken impression rather than an entrenched bias), but attempting to spread it far and wide.
Existing safeguards against this include our concept of expertise. More people will listen to someone who has advanced understanding of an area of knowledge, versus a novice. Usually an expert in a subject really can provide better guidance to form valid opinions.
The trouble arises when you have an expert in an area that is not rationally mappable to reality, e.g. the Bible or religious experience. A preacher can claim expertise on the issue of origins because of biblical knowledge and claims of personal religious experience, without needing to prove that he knows enough biology or basic science to criticize the theory of evolution.
So perhaps we need a norm that criticizes use of authority in one area to make claims in an unrelated area. A preacher’s opinion carries little weight in biology, just as biologists do not typically do much to define religious rhetoric.
Now that you mention it, I have kind of noticed this. Social skills appear to consist of a certain amount of glossing over details that you don’t want to derail the more important thought processes. You don’t mention aloud exactly everything you are thinking, because if you do you end up labeled “dork”.
Writing/typing is a little different because you know in advance that whatever comes out is not going to be percieved immediately by anyone, so it goes through fewer filters at first. Afterwards you have the chance to edit it to be less embarassing (flow or emotion) or more correct (factually or logically).
Overall this means you can reveal more without risking as much. Rather than revealing half-formed thoughts (which people find to be threatening), you can fully develop them before revelation, and make yourself sound sophisticated. Even so, some thoughts are best left out (in some contexts) because they distract from the main point—you can only develop so many concepts in a given amount of space.