I'm finding I actually rather enjoy unraveling sweaters. It has a mindless, meditative quality, with the smooth back-and-forth twisting of the niddy-noddy, and the soft "zzzzzup" of unraveling yarn. It's quite relaxing, as long as there aren't any tangles to pick out.
I suppose I also enjoy the tidying aspect of it--I'm taking an ugly old unwanted sweater and turning it into a smooth, neat, and beautiful skein of yarn. I like to imagine I'm giving these poor discarded sweaters a second chance at life.