A vote for neoliberals is a vote to not have fascism for four more years. America’s voting system doesn’t allow the never-have-fascism votes to be pooled with the delay-fascism votes, so unless there’s a decent chance for a mass swing of voters from delay-fascism to never-have-fascism, trying to encourage a small-scale swing only makes immediate fascism more likely by weakening the only thing with a chance to delay it.
If the plan is to try and encourage the Democrats to have primaries that actually have the power to move the party left, now is not the time to withhold a vote in protest as there’s a good chance that even if it did convince them, there’d never be another election that wasn’t rigged so they’d lose it no matter how popular they were.