> The problem is a strong multiparty system can get fringe elements in power.
But as demonstrated, a two-party system can (will?) eventually lead to polarization, causing one of the only two options in the system to become a fringe element, and unfortunately the only option the people have now are the democrats or a party of right-wing extremists who are anti-woman, anti-poor, anti-education, anti-science, and white supremacists, all while lying about anything they can to make people afraid of anything that will drive them to vote Republican.
In other words, a multi-party system might end up with fringe elements, but we've proven that the two-party system can not only do that but effectively force a huge number of people to vote for that fringe element.