I'd tend to agree with RJ that an email prompt only encourages objectionable behavior between two or more contentious parties. BO's rationale is not convincing. A complete and rational discussion is better served by a timely but measured response and not an immediate emotional knee jerk reaction to an email alert of an opposing viewpoint. 

If the subject matter is important enough to a commenter they will re-open the comments and see what interesting comments might shake out.