Indeed one can be guided by the Holy Ghost, as well as by a demon. There is no assurance of truth outside of the Church with is the very foundation of truth, but that is not saying that everything arrived at privately is necessarily false. Like someone pointed out to me on this thread, I{, or most Catholics do not run to Catechism for every verse either, -- we just read what's written, -- so our reading and interpretation are private at some stage. The difference is that if I interpret the scripture incorrectly, I will take correction from the Church, and one who celebrates his schism will not, anbd so he will perish.
And do you not think that protestants have an ecclesiology? We, too, take correction from the Church.