It's not like a decade of doomerism and nihilism has done anything more than gotten us here in the first place.
Any doctor will tell you that contrary action is the first step towards health
Is it really doomerism and nihilism to blame? You can squarely blame many people for the current shit sandwich but they are not the doomers. Democratic leadership for their delusional attitudes, right wing reactionary think tank shitbags, Facebook uncles, but not Bernie bro straw men.
Easiest way to answer is to ask the converse: what if the centrality of doomerism and nihilism wasn't part of our lives? What would all of those things look like if left leaning folk (really, the majority of the country) took consistent positive action demanding better leadership and representation?
The much easier converse of "what if we all just believe and everyone was more involved" is "what if the democratic leadership wasn't delusional," man. It's not like people are just doing nothing.