I think the word "professional" has been misused, it really means someone who does something as a "profession" like making his or her living from it. And amateur I think means someone who does it for fun and just the love of it.

Many times amateurs are much more masterful and knowledgeable about things than professionals. Unfortunately these words have been used in the wrong context and have found different meanings than what they were intended for. Now many professionals use the word "amateur" to put someone down as unknowledgeable and so on. But this is actually those people's egos and insecurities speaking.