Pilgrim

Certainly those who are teachers are more culpable. But that doesn't necessarily mean that they are not ignorant of the fact that what they are teaching is not biblical.
I have been a Christian long enough to know that there is not one Christian theologian or lay Christian that is 100% correct in their understanding of theology.
In my study of this subject I have read quite a few articles by Reformed believers and although for the most part all are generally on the same page when it comes to the second commandment. There are differences such as what constitutes as worship and what doesn't.
Some say that wearing a t-shirt that has a picture depicting Jesus on it may not be a wise thing to do. However, it may not be symbolizing the worship of Jesus. It may just be that the person wearing the t-shirt is telling the world where their loyalties lie.
This is just one example of some of the teaching I have found by Reformed people.
The fact that teachers are not perfect and can be wrong, makes it all the more important that other Christians come along side them when they believe them to be wrong to try to correct them.
I have read a few articles over the years, with the admission by the person writing that they had previously been in error and hope to now set the record straight.
John Knox used to cry and pray over his sermons before he preached them, lest he lead anyone astray. I believe this is the attitude every pastor/teacher should take.
But that doesn't necessarily safe guard 100% against error.

As to the approach that should be taken against error by a teacher. I favor a probing discussion before making too strong a judgment. But in the end, compromise of the Scriptures shouldn't be an option.
I will also say that sometimes the best person or persons to discuss this with the teacher, is someone who already has their respect.

Tom