‘Catholics feel the protestants are not even part of Christ’s body’
Not true, anyone who has a Christian Baptism and accepts the Nicene Creed is part of the Church, although Protestants are in some greater or lesser error and the Orthodox are in schism.
Well, it is true in many Catholic circles.
If you are not a part of the Catholic church, one is not a part of the true church.
I have heard this countless times as an Anglican.
Clearly those espousing such a thing are in error.