Smileys were introduced to world wide web to supplement lack of body language into typed communication. Since typed words don’t differentiate between tone, humour, sarcasm or insult, it was useful to add appropriate smiley to signal real meaning. It’s been mostly used in right way too, which means to signal that you really are just pulling leg when you might appear taunting, or that you mean well in friendly way when you might appear condescending. Obvious possible drawback, as is case with body language, is the incongruity of smiley and the written content. Smiley can turn a sarcasm into a humour but it cannot turn an abuse into sign of goodwill.
What things have come to being is use of smileys to soften the blow while hitting harder and harder. So you can say all the mean things you want and append with an smiley. If other party retaliates, just point to smiley to show that you didn’t mean it, and he is overreacting. Thus you can have your cake and eat it too. Such double standards in word usage and weakness of commenter to be able to bear result of his accusation and unwillingness to entertain counterarguments are irritating at the best.