LiW already addressed this, but I'd like to offer another perspective. This is a discussion forum. Everyone here has the freedom (and, indeed, the responsibility) to weigh what is written against Scripture. When someone is continually posting the same (or similar) message, that might be considered "preaching". When someone mentions an idea once or twice, it can hardly be considered such.
There are many people on here, all at different levels of understanding, faith, and ability. If we were to hold everyone to the standard of Ephesians 4 Teacher, this site would cease to exist in a hurry. Let's be gracious with one another, striving to understand first and then, where it is warranted, questioning, challenging, or criticizing.
By the way, although discussions do get heated here in the Family forum at times, the Bible Discussion forum is usually the place where people express strong opinions. That way, the rest of the site remains friendly and edifying.