Exactly right. I'm a bit confused by Irvine on this point because he has been one of the strongest advocates of compromise and finding middle ground rather than lofty goals and preaching to the far left/right converted a la Sanders for example. And yet the two-party system in the US as it is right now is breeding ground for little more than contempt and entrenching yourself in ideology. You win - you make it your job to stick it to the other side until the next election. You lose - you make it your job to obstruct. It has resulted in a government almost entirely unable or unwilling to get big things done. If you introduced a third or fourth party even with relatively small numbers of seats, you would see a fairly quick turnaround in attitude. And frankly if you look at other Western democracies generally speaking there tend to be 2 major parties (typically centre-left and centre-right) with one or more parties to the left and right of those which are almost never in power except in extraordinary circumstances and then often for a short period of time. BUT they are enough to get more interesting legislation passed.
I think the stereotypical view of 78 Italian parties with members in fisticuffs in parliament is not at all representative of what actually goes on.