And heck, I'm far too ignorant to say that they aren't right. It could be that our fossil fuel consumption will cause a feedback mechanism that will lead to a new Permian Extinction. Or the feedback loops may be largely self correcting. If the former, anyone who doesn't do something right now is suicidal...
Or those who believe Fukushima will kill half of humanity without some dramatic action. To them, not rising up in some way would be incredibly irresponsible.
And there are plenty of other examples, some of the science fiction disaster movie sort, some along the lines of Sodom & Gomorrah.
Have to pick your battles, as you say. But people tend to pick those they think worth fighting for largely based on a deep emotional response, which does not always lead to the right choice.
But it's really really important!