I guess I see that kind of attitude as the primary thing and then arguments like climate change etc as post-fact justification.
Humanity has been and always will be a mix of beautiful and terrible. In the same time window you're talking about, we made huge strides in equality, science, reached for the starts, explored the depth, etc.
Go back decades, centuries and millennia and you will find something to be depressed about. Crusades? Slavery? Pandemics? Wars? Those things have existed for ever, and yet humanity has always found a way to move forward, trending towards better/safer/more equal. If you believe that "humans are as cancer", you are as justified today as you had ever been, but as a human, forgive me for not being interested when someone who loathes my species suggests it'd be better if we died out.