Why Do You Think Your Opinion Matters?

Two Questions: Why do people seem to think that their opinion some how affects what is or is not the actual truth? Secondly, the majority of arguments I see for or against a given belief are based on the quality or lack of quality of that belief's believers, which is not even a valid argument. For the most part, the legitimacy and accuracy of an argument is not in any way affected by the quality of its supporters.