This is a profound misunderstanding of how electoral politics works. Progressives need to primary moderate Dems in safe seats because the energy and grassroots support they bring, along with their full throated advocacy of progressive policy drags the Overton window to the left and makes it easier to get moderate Dems elected in swing districts and works to eventually turn red districts purple.

The GOPs success in the last 30 years has come from dragging the center to the right in exactly this way. Progressives are vital in dragging it back to the left to the benefit of even moderate Dems. That is why Republicans never punch right. Moderate Democrats need to learn to stop punching left and only ever punch right if they want to stop getting repeatedly Charlie Browned by the GOP.