I find that an argument is necessary when the arguer seeks to dispel ignorance, learn more about an opposing viewpoint, or open a discussion about the issue.
If the person making the argument has not considered other viewpoints, the point made will lack support. The argument will not be convincing if these alternative views are not refuted. Therefore, any argument that does not consider other takes on the issue is an unnecessary one. This would be a time when making an argument would be a mistake; no consideration has been given to a resistant audience.
Other stances on the issue should be considered by the arguer even if the issue itself seems to be very bipartisan. By learning more about the opposition, the arguer can understand where they come from and better mold his / her own argument. For example, doctors should consider why some parents are against vaccination. Instead of dismissing these parents as a lost cause, doctors should address the reasons people resist vaccination and pose their arguments to refute these reasons.
An argument can be both necessary and a mistake, therefore, when it it attempts to dispel ignorance but lacks support through not addressing or considering other opinions. Doctors advocating for vaccination is a very necessary argument, but they must make sure to acknowledge the opposition’s fears. By creating a well-rounded argument that recognizes other opinions, arguers can create necessary and convincing statements.