Why is a two party system for the U.S. important?

It might be best said this way. The Republican party sort of acts like a Grandmother that is too conservative and closed minded. However, her presence also allows her grandchildren to have enough money to go to college because of that conservative close minded approach to life. So, the Grandchildren: "Democrats" become progressive and help the poor and become educated and more progressive while the Grandmother stays close minded and makes sure she has enough money to keep her kids in school and to pay the military and police so she and her grandchildren are safe from all potential attackers in the U.S. and abroad.

This is how it all has worked so far. But now, grandmother and all her friends are getting old and dying out and her grandchildren are too idealistic and may be bamboozled by criminals here in the U.S. and abroad.

How will the U.S. survive all this?