On-line communication is a tricky thing. Without tones of voice, facial expressions, body language, etc. it is often difficult to convey meaning.
The effort of having to type out something versus speaking adds to the difficulty. This is especially true when trying to convince someone of a certain point of view.
This is a fairly popular web page on the Internt for learning how to avoid common pitfalls in constructive a logical assertion (or argument).
http://education.gsu.edu/spehar/FOCUS/EdPsy/misc/Fallacies.htm
