As written by whom? The original authors? The current NIV? You have made an excellent point that if one does not interpret through the eyes of the consensus patrum, then that interpretation can support, why, any heresy that can be imagined by men, and influenced by the lord of this world.
The Holy Scripture is inerrant as written by the original authors at the time they wrote them with the intention they wrote them, for the audience they intended. This does not mean our understanding of the scripture today is inerrant, but we have tools to approximate it by referring to the interpretation we can glean from the Fathers of the Church.
Reading the scripture according to the Protestant charlatan-a-day is virtually guaranteed to be false since they assume their own interpretative authority in the light of, at the oldest, traditions of 15c, which is after any cultural continuity with the Apostolic times was long lost.