I wonder if Protestants view Mormonism like Catholics view Protestantism. This thread seems to point in that direction.
We don't and for several reasons, one there's several different version of Protestantism, there's not a central authority deciding inter-sectrial doctrine.
But also from a religious standpoint there's a giant difference. Protestants and Catholics use the same scriptures with the difference lying in the interpretation and the fact that protestants does not recognise the bishop of Rome as God's sole representant on Earth.
Mormons on the other hand use new scriptures, they have prophets and a radical different doctrine which lies outside the Nicene Creed. As such one of the few things Catholic and Protestant theologians agree on, is that they recognise each others as Christians (with a few groups as exceptions) and that Mormons (and Jehovah's Witnesses) are not.