A one-sided argument a variant of the logical fallacy known as special pleading. In this variant, only the reasons supporting a proposition are supplied, while all reasons opposing it are omitted.

"The one-sidedness fallacy does not make an argument invalid. It may not even make the argument unsound. The fallacy consists in persuading readers, and perhaps ourselves, that we have said enough to tilt the scale of evidence and therefore enough to justify a judgment. If we have been one-sided, though, then we haven't yet said enough to justify a judgment. The arguments on the other side may be stronger than our own. We won't know until we examine them. So the one-sidedness fallacy doesn't mean that your premises are false or irrelevant, only that they are incomplete." [1]

"With rational messages, you need to decide if you want to use a one-sided argument or a two-sided argument. A one-sided argument only presents the pro side of the argument, while a two-sided argument presents both sides. Which one you use will depend on which one meets your needs and the type of audience. Generally, one-sided arguments are better with audiences already favorable to your message. Two-sided arguments are best with audiences who are opposed to your argument, are better educated or have already been exposed to counter arguments." [2]

Links

• The One-Sidedness Fallacy - Peter Suber, Philosophy Department, Earlham College
• Developing a Promotional Strategy - Michigan State University, Extension Bulletin E-1939