I used to have a professor who after making a contentious point, would pause a moment and wait for any rebuttal from the students attending his lecture. If no one spoke up, he would always say, "Silence is affirmation."
He was a brilliant instructor and i think many of his students were in awe of him, and maybe a little intimidated as well. Those might have been the more likely reasons behind the silence, rather than absolute agreement to every idea he put forth.
Silence isn't affirmation. It isn't withdrawal, anger, stupidity, death, or anything else for that matter. Silence isn't anything. It is the absence of something, and nothing more. Silence is subtraction in a society that emphasizes addition, and therefore is constantly misunderstood.