Because you should be pragmatic. Voting democrat, typically, may not get you your more progressive policies, but what it won't get you, are regressive policies. It IS a compromise. Here is what I think Green voters should do. If the state is a Red or Blue stronghold, as in, no matter what you do, it's going to be Red or Blue, vote Green. It cannot hurt, and there are only upsides. If you're in a tightly contested state. Look at the policies on offer, and decide which of the two candidates are less likely to do something disastrous. Can you live with yourself if you vote Green, Green ends up with 5% overall and the election is decided by a few hundred votes, and then the winner rolls back environmental protections, and pumps state money into subsidizing coal mining? Or something equally regressive? If you're ok with that, then that is what I would call, cutting off your nose to spite your face.