That was exactly the point of those you are debating. When the solar is not outputting any power, the utility must be able to provide the generation, and have the system capacity from the generators all the way to the solar customers. They must be able to do this (as it always has been) while making less money because the utility has sold less power to the solar cutomers during the day.
Boy oh boy, You are forgetting that the POCO is gaining a benifit of the solar provider at the same time they want to penalize that person. This is capitalisim at is best.