I think forgiveness is the biggest form of human weakness. Anyone who forgives is only enabling his/her attackers in the process.
It's not about moral or immoral. There is no such thing as objective morality, so the basic premise of your question is unstable. Forgiveness is strategically a bad move and no poweful society should encourage it.

As an example, Americans made a mistake by freeing Negro slaves and expecting them to integrate. Nature has no room for forgiveness or sympathy. What should have been done was all Negroids dumped back to Africa. Or perhaps, all should have been exterminated and a massive cover-up effort should have been launched by the government. Remember, there is a reason why the military and the press both were controlled by the same ministers in powerful kingdoms in the past. The only version of news/history is the victorious king's version!