Forgiveness is a moral virtue as is justice, kindness, and love. So, let us ask the question in a different way: Can we ever have too much justice? The answer is no. How can someone be fair to an excessive degree? Can we have too much courage? Again, the answer is no. We can distort courage, or any other virtue, by engaging in one of the vices associated with a given virtue. One vice associated with courage is reckless bravado. In the name of courage, a person who is a non-swimmer, for example, might jump in a stormy sea to save a drowning dog. This is not courage, but instead is reckless bravado, an unwise exaggeration of courage.
So, as we cannot have too much of a genuine virtue, as we explained with our example of justice, it seems that we cannot have too much forgiveness, either. A lot of goodness is not a bad thing.
As we saw in the example of courage, what we have to guard against is one of the vices associated with a given virtue. One such vice connected to forgiveness is excessive submissiveness, as we let others take advantage of us. Yet, as we can see, this is not a problem of forgiveness itself, but of the distortion of forgiveness.