What argument is the author putting forth?

One important argument is that the slave owner suffers more than the slave. From a moral standpoint, this is actually an interesting point of view from this period of time. Douglass proved that African-Americans were capable of learning and deep thinking; when Mrs. Auld was forbidden to teach him, it hurt her because it took away her logical ability to consider all humans as humans regardless of race.

I think one of his major arguments is that it is ignorance which perpetuates slavery for both blacks and whites. One of the most important ways slaves were kept in bondage was not simply the threat of physical brutality; rather, it was through deep and sustained ignorance. Slaves were not allowed to read and write and were thus generally not aware of the events outside of the plantation, could not communicate with each other well to foment rebellion or conduct escape plans, and could not attain the sense of self-sufficiency and pride that came from being lettered. Literacy brought with it an understanding of the larger world. It opened up before a slave the idea of justice and an understanding of history. Reading the Bible led to a truer comprehension of Christianity. Check out this link,

http://www.gradesaver.com/narrative-of-the-life-of-frederick-douglass-an-american-slave-written-by-himself/study-guide/major-themes/