Thin difference between responding and reacting.
a response... Responding involves taking on board what someone else has said. It involves considering the information and agreeing or coming up with an intelligent counter claim based on actual knowledge and critical thinking. Responding is using head and intelligence. Responding does not contain personal insults in the same way the reacting may.
Reacting doesn't involve taking on board what someone has said. It does not require to consider the arguments or point of view. Reacting allows for unintelligent claims. Reacting is based on emotions rather than reason. Reacting often involves the affirmation that one is correct and insults those that disagree.
(From Sources)SN (a 1992 pensioner)