As a thought experiment ask yourself what you think would happen in the following scenario:
We enshrine the two party system into law but allow all Americans to chose their party freely each year. You no longer pay taxes or receive services from the government but from your party instead.
Do you think this would lead to harmony where the half of the country that wants high taxes and many services would join the D party and the half that wants low taxes and few services would join the R party, all living side by side in harmony?
Or do you think this would lead to total chaos where the people with money to take (IE money to spend on services for themselves) all join the R party and the people without money to take all join the D party looking for services they can’t provide to themselves.
I would say it’s pretty obvious what would happen but then again my world view is a bit cynical and of course not the only one. I would say it’s exactly what has happened to our system without needing the thought experiment to make the incentives obvious.