He is entirely wrong.
Which fundamentalists are you talking about? The ones who accept the scriptures to be inerrant? That is the classical definition of fundamentalism. How has an adherence to the fundamentals of the faith marginalized and paralyzed Christianity.
Carter is an idiot. Adherence to the fundamentals of the faith does not marginalize Christianity from Christians, but it will ALWAYS marginalize Christianity from secularism and humanism and liberalism.
Fundamentalism is defined by more than that, and including a separatist element