Many speakers and writers deliver speeches and articles without being aware of what kinds of people are in their target audience. This can be disastrous.
A good example of a writer not knowing her audience would be an Intelligent Design advocate or a young-Earth creationist writing an article to be submitted to a prestigious journal such as SCIENTIFIC AMERICAN or SCIENCE. The writer would have no serious chance of being published unless the editors of such journals wanted to warn their readers about what NOT to accept.
When submitting articles, writers should know what kinds of journals in which they are seeking publication, who the general readers are, the philosophy of the editors of the journal, etc. This way, even if the writer wants to address an audience that could be hostile to her message, she could still tailor the message in such a way that it would receive less hostility, or possibly, even acceptance.