The alternative involves progressives mobilizing and organizing like conservatives. Providing the sort of funding that would allow Democrats to abandon corporate funding and aipac funding. Voting solidly and regularly as if their life depended on it, because it does. Just like conservatives do. Which progressives don't.
Democrats treat progressives like constituents. The problem is you want them to treat you like their only constituents. But you aren't. Neither can you justify it currently. The Democratic party For Better or For Worse is a coalition. A very diverse coalition with wildly disparate views.
The party moves to the right in order to get Republican votes. It tells progressives they have no choice. They don't treat progressives like constituents. They treat us like hostages.