Yes, kindness should be reciprocated, because that is what humanity is all about. It is important that people help each other. If one person helps someone, that person can help someone else, and there will be an ongoing cycle of assistance. This makes humanity a happier place because we can all depend on each other.
Kindness should be reciprocated simply because that is the moral thing to do. The more kindness there is in the world, the less violence there will be. If kindness isn't reciprocated, it should be paid forward to someone else. Just a simple act of kindness can make a huge difference in someone's life, so pass it on!