What does Douglass think of the "underground railroad," and why?

Douglass feels the underground railroad is too publicized. He also feels that although the intent is honorable, the slaves themselves are lost when they attain their freedom.... they're unprepared. He also believed that the publicity that accompanied the underground railroad made the slave owners all the more aware, and that the owner's awareness was a hindrance to the desired result.

From the text:

I have never approved of the very public manner in which some of our western friends have conducted what they call the underground railroad, but which I think, by their open declarations, has been made most emphatically the upper-ground railroad. I honor those good men and women for their noble daring, and applaud them for willingly subjecting themselves to bloody persecution, by openly avowing their participation in the escape of slaves. I, however, can see very little good resulting from such a course, either to themselves or the slaves escaping; while, upon the other hand, I see and feel assured that those open declarations are a positive evil to the slaves remaining, who are seeking to escape. They do nothing towards enlightening the slave, whilst they do much towards enlightening the master. They stimulate him to greater watchfulness, and enhance his power to capture his slave. We owe something to the slave south of the line as well as to those north of it; and in aiding the latter on their way to freedom, we should be careful to do nothing which would be likely to hinder the former from escaping from slavery.