This is very important, and I'm glad this person understands that we don't express forgiveness indiscriminately. It is really not showing Compassion to that other person, if they have not acknowledged wrong doing and had regret, to actually express forgiveness to them because they may learn that unbeneficial actions don't have an unbeneficial result. So, the most important thing is to forgive their actions within our mind and heart but to express forgiveness may not be skillful. This is considering the broader picture of compassion for this person and compassion for anybody else this person may do these actions towards.
The expression of forgiveness has to be balanced with wisdom to know when it is appropriate to express forgiveness of others. Especially if they are harming other people. This can actually just encourage them to continue unskillful actions. They have to acknowledge responsibility for their particular wrong doing and be held accountable for it. Otherwise, it can encourage abusive actions to continue.