Orbe Phillips [one of the radical Reformers/Anabaptists], rejecting the idea that 'the body of Christ had been made by Mary (as the world thinks and says with such want of understanding regarding it),' asserted instead that 'God, the Heavenly Father, prepared for Jesus Christ his only begotten Son, a body (Heb. 10:5), but not of corrupt human seed (Luke 1:35), rather of his incorruptible seed.' For, he continued, 'it is impossible for the flesh of Christ to be formed of the seed of Mary; for neither the seed of Mary, nor that of any earthly creature can by any means be the true living bread that came down from heaven...or be so called.' [p. 156f]Now of course this was not the prevailing opinion of the Protestant reformers. But it should be said that unless we "read the Scripture within the living Tradition of the whole Church" (CCC §113) we have no moorings to prevent us from reaching false conclusions such as these. As we've seen before, letting Scripture interpret Scripture is no solution to this problem precisely because (apart from Sacred Tradition) there is no solid reason to interpret one passage in light of another (rather than vice versa). The Bible does not contain the keys to help us with this.
Now it should also be said that Protestants actually do read the Scripture within their own traditions. This is why Baptists reach Baptistic conclusions, and Presbyterians reach Presbyterian ones, Methodists reach Methodist ones, and Lutherans reach Lutheran ones. And the fact that they have inherited a great deal from the Mother Church whence they came is why they are right about many things. I suppose the appropriate question to ask, then, is: why would we accept any of these traditions, coming 1500 years or more after the founding of the Church, in preference to the Sacred Tradition of the Catholic Church that has been there from the beginning? The Protestant reformers rejected this, preferring to formulate their own theological traditions, but - as we see in the case of Orbe Phillips above - once Sacred Tradition has been abandoned, there is no good reason to stand with Luther or Calvin rather than to go off on one's own.