Funny how you you complain about evidence-based debates proceed to mischaracterize the U.S. based on your impressions.
Americans are not all of the same opinion. They do not all use the same arguments which have the same faults. In this they are like all people everywhere. Also, their political parties do not all employ the same arguments with the same faults. Arguing that everyone has the same faults is both-siderism. It is a counsel of despair. In fact, each party will use facts and international comparisons when doing so supports their preferred policy.
The Democrats have been quite fond of international comparisons in support of their efforts to improve healthcare. I struggle to find a topic on which Republicans prefer facts to mythology but they certainly grab onto a fact when it supports what they want to do. They can recognize and employ a good argument if it presents itself.
If you hear someone making a stupid argument, regarding health care or whatever, nine times out of ten it is not because they desire a worthy thing and are too stupid to get it but because they desire an unworthy thing and are crafty enough to recognize a plausible cover story. You can recognize this happening when someone drives for a constant goal but changes arguments as suits the moment. Republican arguments for lowering taxes fit this pattern as do arguments for not doing anything about climate change.
It isn't the stupidity of politicians, or even their voters, that explain American policy. It's disharmony within the nation mixed with political institutions that expect people to work toward a common purpose.