I'd think it's part o our nature as a social species. Let's put the larger issues to the side for a minute. Why do people rant to others about the shitty day they had? What about rumors, gossip, etc? Things that people really don't care about, but for some reason like to hear. Now this doesn't apply to everyone of course, but it's big enough to be considered normal.
We are supposed to care if people are dying overseas from things we have little to no control over and will likely never affect our lives. The misfortune of humans is something we are supposed to care about, like if a factory closes down and hundreds are laid off, even if it's in a different country. We are expected to drop our loose change in to the cups of beggars despite there being little chance that it will help us. These are band-aid solutions to problems that have already begun.
Yet when we get upset over things that we feel may have a negative effect in the future, we are told to drop it, it doesn't affect us. Should we wait until it does? Remain silent until the damage is done? We are expected to care about domestic abuse victims today, but we're not supposed to rag on something that we thing will lead to it? If we see our culture/society/industry going in a direction we do not like, should we remain silent until it has finished changing?
I'll agree that many things are overblown and moderation should be used, but there are a lot of people, all of them passionate about different things. However it's up to each individual how worked up they get over something, and merely because not everyone shares the same passion does not mean they should be quiet. Respectful, yes, but there's no clear place to draw the line that I see.
