The primary is the only time to drag Biden left, and even then it's likely he ignores his campaign promises if elected.
Telling people they can't even do that, is just going to make them give up and become disengaged.
Biden isn't a strong enough candidate to do that, he barely beat trump last election. He had plenty of popular votes extra, but because the electoral college is a thing, if trump got like 30k more votes in 3 states, Trump would have won again. Biden needs every vote he can get.
Pretending everything will be fine so we don't have to do anything doesn't work for climate change and it doesn't work for elections.