While you might quibble with his exact wording, the truth is that Fr. Longenecker's overarching point is correct.
I'm sure you've met plenty of folks for whom the "Holy Spirit" has a way of just happening to go along with what they wanted in the first place. Perhaps that's even happened a time or to to you, as it has to me.
Whether we acknowledge it or not, how we receive and interpret Scripture, really is guided by various factors in our own lives.
A church may not be a perfect guide -- being populated by humans, how could it be? But it's almost always a more reliable guide than the nice folks on TV or wherever.
There little doubt that, there are many quacks Quibbling queerly..
Actually, if this argumentation is the result of the submision to Rome then it is an argument against it.
Longenecker seeks to broad brush all non-Catholics together, as if Anglicans are actually pouring over their Bibles, while he equate the pure subjectivism of Mormon proselytism with his former baptist teacher who told him to prayerfully search the Scriptures, and which method he either implicitly sanctions by saying it led him to Rome, or he was led by the Holy Spirit to Rome by the using the same fallible human reasoning he censures as unreliable!
And then in its place and he advocates “one that claims to be directed and guided by the Holy Spirit.” And although this authority can claim more historicity than the Mormonic “living prophet,” its “infallible” interpretation of Scripture, history and tradition are no more open to debate or requires demonstrable Scriptural warrant than theirs are, and in reality its authority rests upon its own proclamation. According to its interpretation, only its interpretation can be right in any conflict.
Thus we are much back to square one, and the assuredly infallible magisterium of Rome can communally but autocratically channel truth just like the autocratic Protestant he characterizes as doing. Except that for Rome this also includes infallibly tweaking the concept of tradition* from what was understood early on, as well as defining “unanimous consent of the Fathers”** to make something much less than that.
The difference here is that the authority of the apostles, who appealed to human consciences by “manifestation of the truth,” (2Cor. 4:2) and who added to a yet open canon, was established by a purity and teaching that conformed that which was written (unlike such things as praying to an heavenly object besides God), with abundant supernatural attestation, (2Cor. 6:1-10; 12:12; Acts 17:2,11; 28:23)and was not based upon formulaic assuredly infallibility.
Ad paradoxically, those who contend for Sola Scriptura will agre that the modern trend toward baptized subjectivism is contrary to Scripture, and that eccelsial community and its magisterium is necessary for perfection, but that only the Scriptures are infallible, and teaching is established as authoritatve by its conformity with Scripture and ts attestation.
*http://www.christiantruth.com/articles/livingtradition.html
**http://www.equip.org/PDF/DC170-3.pdf