Getting rid of one party in a First Past The Post system would result in another party taking its place.
Exactly. Get rid of the Republicans and another obstructionist party would eventually take their place, putting us right back where we are right now. You want to replace the first-past-the-post electoral system with one of proportional representation and political plurality? Fine, but how do you plan on accomplishing that with the Republicans, or some other obstructionist fighting you at every turn?