What we have here is a misunderstanding of tact. In order to convert supporters of one line of thinking to another you must only be a catalyst for a thought process that will lead them to convert themselves. It is called the powerful art of gentle persuasion, not the gentle art of powerful persuasion. When you attack others thoughts on the subject at hand, conclusions that they have come to based on the best information they have and/or are willing to aquire, many will receive this criticism as an assault on their own intelligence, and in order to save face, will only dig deeper to justify their positions and will likely respond in a manner that is less than friendly.