If you don't expect it to be printed, write it anyway and share it with other people. Maybe they would like to write a letter as well or sign your letter. At the least they would learn something. Consider using the letter to show your solidarity with people or issues by sending copies to appropriate institutions. When replying to a specific piece, use Email since it is an instant reply.
Fax is also useful for speed.
Only mail a letter if you have no other way of contacting the journalist or if you include extensive documentation. Time is usually of the utmost important. You can send an Email and also mail a copy. To clarify for yourself what your thoughts are. To learn more about the subject To get a countervailing argument or information into the minds of the public To show the reporter or editor that you are paying attention to what they produce To inform the reporter or editor on a subject where they have inadequate information How to write Begin with the title of the story or editorial you are replying to and the date it appeared.