It wouldn't sound good. The piano player would learn not to count on the white keys and only use the black keys. So, it is in church with undevoted Christians. They scratch their heads and wonder why they are so unfulfilled. Church leadership learns to no count on them and only use the committed ones.
Harmony comes from devotion.
Because, I am called to be devoted and live in harmony with other believers. This is God's will for our lives. There is safety in numbers. 2 cords bound together are stronger than one lone strand of fiber. God yes, Church no.