Many of our emotions are driven by a need to protect our own identities: envy, pride, shame, anger... because they're private and (by definition) selfish they often get a bad rep but this isn't always earned.

There are other emotions which are driven by our membership in a group of people and gain strength from the massive value that belonging entails (to normal people). Those are some of the most sublime emotions we have: patriotism, empathy, group hilarity, self-sacrificial courage, the urge to behave selflessly in an an emergency (although they can become incredibly dark and deranged when applied to fear or violence). I think the feeling you describe is one of the second group of emotions: it feels profound, and pure because it IS pure. It is a specific instance of deep care for other people (as individuals and as a class) and an expression of true empathy. It feels so strangely impactful because it is bringing you completely outside of yourself and that is a rare experience these days. It wasn't always so.