Teachers have a credential that proves they are highly invested in their subject matter. But by design the overwhelming majority of students will not share a similar interest. Kids intuitively know that school is not only for learning, but sorting and selection. James Herndon know. It was Noman.
Red ink is as indigenous to teaching as unreadable prescriptions to medical doctors.
And like unreadable prescriptions, red ink is dangerous. All the research I've seen indicate students learn better with encouragement and that red ink is discouraging. I am indebted to Al Grommon, a former professor of mine, and former president of the National Teachers of English. He taught us to write positive comments in pencil so we could erase them if we found we'd been harsh instead of constructive. Many, if not most, books on discipline recommend making conditional statements to students.