Ah, I see. You think that democrats will change if we just stop voting for them. They wont. As I said, they're essentially just Republican lite. We'll either have 2 parties that are almost the same, or the democratic party will simply dissolve and we'll just have 2 identical republicans running for office. Either way, yes, we will have to bring about change with organized resistance.
However, in the case that the ruling class still allows for the republican-lite party, it's better to let the democrats keep only mostly destroying the world instead of letting the republicans openly see how quickly they can tear everything down, because that leaves less rebuilding we'll need to do when the time comes for that. Refusing to vote for the lesser evil is like refusing to eat what meager rations you get from your jailers as you work toward your jailbreak - you'd be a fool to deny it simply because it's part of the system you plan to dismantle, because your task will be harder for it.