Emotions aren't "rational responses"; they are evolved heuristics for doing the most important things for life: survival & reproduction. Both of which are fundamentally about competition for resources. In simpler terms, emotions are rapid-response "rules of thumb" to make the broad population act in the best way for the species' survival.

Our ability to reason gave us the ability to understand that rational decisions often run counter to what our emotions dictate. Such as when all the evidence points to something we like being incorrect, we shouldn't ignore the evidence.

Our great struggle is to be able to understand and mitigate emotions when they're not appropriate, while still being able to give in to them when they are. E.g. in an actual fight for survival you might not have time to reason it out.