Not just different things, but whether those things even exist
Like, I'm all about debating the best approaches to fighting climate change. I'm not about debating whether it exists.
You can't debate solutions when you disagree about what the problem is
They are arguing that a real progressive would try to fix democracy. Overturn citizens United. Get money out of politics. Push for an alternative to first past the post. Remove the electoral college. You do those things and fascism becomes much easier to defend against.