You'll have to decide for yourself which side of the argument you are on.
The reasons to prosecute Nixon would have been because he participated in a cover-up of criminal activity (the Watergate break-ins). He had abused the power of his office and damaged the respect Americans had for government. He had acted as though the president was above the law, and prosecuting him would have proven that is not true.
On the other hand, President Ford (who took over after Nixon resigned) felt the nation had been through enough pain already and that healing was needed, as the question noted. In the text of his proclamation of the pardon of Nixon, Ford stated, "The tranquility to which this nation has been restored by the events of recent weeks could be irreparably lost by the prospects of bringing to trial a former President of the United States. The prospects of such trial will cause prolonged and divisive debate over the propriety of exposing to further punishment and degradation a man who has already paid the unprecedented penalty of relinquishing the highest elective office of the United States."
If it helps you decide, in 2001 the John F. Kennedy Library Foundation presented Gerald Ford with the John F. Kennedy Profile in Courage Award for his pardon of Nixon. Senator Ted Kennedy presented the award to Ford, noting that in the opinion of the Kennedy Foundation, history had proven Ford right about his decision in the matter.
