Is self defense really self defense, or is it a code word for learning how to harm others?
Is it really possible to directly thwart the efforts of someone who is trying to hurt you, or is it necessary to actually inflict harm upon them, thus interfering with their ability to cause you harm?
There is a distinction, at least in theory. We can train our bodies to be more resilient, to protect our joints, to maintain structure and balance in the face of disturbances, thus making us better able to withstand applied forces and respond to unexpected changes in momentum.
Ultimately, whether reciprocal violence is called for and whether you are willing to apply it is always a personal call in any given situation. But it is worth taking some time to reflect on the question in a general way.
One of my favorite blogs on the subject is Target Focus Training.