One the one hand I don't like the word "hysteria" in this case. According to Merriam-Webster a hysteric person is an "overemotional or unstable person" – I don't see why this should be applied as a whole to everybody who follows science and acts accordingly.

That brings me to the second part: One the other hand it is quite clear (to me) that there is imminent grave danger. Yes, the planet (and maybe some species) will survive. But the temperature rise is unprecedented. Really unprecedented! Maybe only comparable to major events that killed almost all inhabitants on earth (think dinosaurs). Yes, individual humans are able to adapt, but humans as a whole can't adapt quickly. An individual human lives decades and usually don't change much within a lifespan. Cities are built for centuries and societies emerged during an even longer timespan. Rising sea levels and rising temperatures will create changes, most people can't adapt to. It is very probable that those changes will cause uprisings, violance and war.

I don't think that centralized action is the only solution, but maybe a part of it. In the end also centralized action needs to have decentralized supporters (at least in a democracy). So building awareness of the imminent danger is important. And that's what climate activists do.