Luther always considered himself part of the Church Catholic.
And Jews consider themselves true followers of God. Difference?
My point is that doctrine needs to be defined in accordance with what scripture says, and such doctrinal declarations have authority and weight BECAUSE they are scripturally sound.
Because majority thinks they are scripturally sound? There is virtually no definition beside appealing to opinion of people who don’t even hold authority to preach like Apostles or their successors do.
It is not a circular argument on its face to say someone is in error if it can be established by objective evidence that someone is indeed in error.
While we can use objective evidence to establish someone as thief, we appeal to juridical system and judges- those hold authority to proclaim evidence as objective and true or not. In your system, everybody is a judge and that either suggests relativism or contradicts Scripture- Peter tells us to not hold to our own interpretations, but those of Church and Lord requires certainty of faith from Apostle Thomas- if there is only opinion, how do we get certainty? Our own abilities are very limited in this sense. After all, if everybody were able to make objectively right pronouncement based on Scripture, there wouldn’t be that many Protestant denominations with different opinions. Without authority to interpret something as metaphysical and full of parables as Scripture (written by people in different time of different cultures) infallibly, there is virtually no way to get it right and be sure about it.
Luther did not attempt to make himself the infallible authority
No, he made himself the interpreter though. Luther also based many things on Scriptural interpretation and later changed them, he allowed Duke of Saxony to practice polygamy because he did not want to lose his political support (and based it on being his religious head too). I do not want to point fingers there, but Luther’s interpretation of Scripture was not objective either. If we believe we are more objective than direct successors of Apostles, their successors or their successors (and etc etc), where does that put us? Humility and obedience are both virtues, I’m sure you would agree.
As a person with at least average reading comprehension skills, who has access to scripture, and is a baptized believer, then yes, I think my judgment on whether something is supported or not supported by scripture can be valid
I believe Popes have been baptized, could read and were believers. Popes affirm Catholicism. Why are they wrong then? If I say you misinterpret Scripture, what authority do we appeal to, beside ourselves?