Objectivity
The arguments presented in psychology papers must be objective. You should present balanced arguments without subjective bias. If there are data to support two or more competing points of view, do not present only the data that supports your own opinion. If one set of data is more convincing, then explain why.
See also: cite your sources
Example:
(Note: the following example was composed for illustrative purposes only and is not factual)
As public awareness of Factitious Disorder by Proxy has increased, a number of accused child abusers have claimed to suffer from this disorder in attempts to avoid punishment (Black, 1996; Green, 1997; White, 1995). These data suggest that, if Factitious Disorder by Proxy is deemed to be a mental illness, child abusers may no longer be tried or punished for abuse that is presently considered to be a crime. Nevertheless, the results of the Jones and Smith (1995) study imply that including Factitious Disorder by Proxy in the next edition of the DSM would increase awareness of the problem among health professionals, leading ultimately to the protection of countless children who would otherwise fall victim to abuse.