Wa alaikum salaam Ahmad,
This is a very good question ... I am just thinking out aloud. It is our duty to fight against injustice, persecution and aggression (2:191-194, 22:39-40). But the moment the aggression or persecution ceases, we should cease all hostilities (8:61, 2:190,192.193). If forgiving the oppressor in a "position of weakness" encourages or exacerbates the oppression or injustice, and will not help bring it to a stop, then our first priority should be to stop the oppression. Once the oppression has ceased, and we are considering how to punish the oppressor for his misdeeds, thats when forgiveness would be better.
Does this make sense?