And if the only "reasonable choice" for political opponents is to abstain from election - sorry, it's not a democracy, but a mild form of dictatorship...
How do you propose forcing competition on an area? If everyone in that particular area agrees on a core set of issues, who are you to tell them that is bad? Is it their fault there is no other party that can appeal to those people? Our system fosters only 2 major parties, and the other is in some ways the polar opposite. That is just how things worked out. As for "mild dictatorship," that seems like hyperbole at best. No one is throwing out elections or ballots, or jailing local opposition politicians, or what have you. Just because it is one party rule doesn't mean it is a dictatorship.
If people want to change the balance of power there, perhaps it is time to redesign the way we conduct elections, moving to one of the plenty of better designs that exist that would foster more, better choices. Of course, even then, there is no guarantee that you end up with anything but "far left" and "left" choices there. If those beliefs are the overwhelmingly consensus there, then it is what it is.