Why would it cause someone to waste their life in misery? On a personal level, for everyone, doom is imminent and everything is pointless - 100 years is nothing, we all will die sooner or later. On larger time scales, doom is imminent and everything is pointless - even if everything was perfect, humans aren't going to last forever. Do people waste their lives in misery in the face of that reality? Why would believing humans are likely to wipe themselves out due to climate change lead to misery?

If anything, avoiding acknowledging the reality and risk of climate change because of the fear of what it might mean, is miserable.