What's so special about being a designer?

It's a simple question for which I am trying to get a clear answer to: can everyone be a designer? It's a fact that everyone has opinions when it comes to design - clients, partners, mothers, grandmothers, uncles, cousins, etc. However, I don't think that design is based on opinions. So, apart from some technical knowledge, why is the designer the authority on design? What makes a designer different from the common mortal?