Why should we take sides on this? For those who reject forgiveness, there are other approaches. For those who view assertiveness approaches as too harsh, there is forgiveness.
Regarding research, we respectfully disagree. You can find the research based on forgiveness therapy with adults at: Peer Reviewed Experimental Studies. You can find the research based on forgiveness education with children and adolescents at: Journal Articles on Forgiveness Education. As you will see, the research shows that those who forgive experience considerable emotional healing.
Finally, forgiveness is not a passive activity. It is an active struggle to love through pain, hardly an inactive approach.