I think you could have made the same argument for laser printers. Who ever said, "Boy I wish I could have my printouts look like they came from a professional printer"? Yet, now they cost $400 and many people have them in their homes. And even those that do not have ink jets with output quality almost as good.

Increased functionality: I can have exactly what I want. It can look exactly like it was professionally created.

Decreased costs: It saves the cost of shipping it from China, then driving it on the freeway. This might be worth it for heavier items. If 3D printing can be scaled to a factory level, this might be very attractive, since you wouldn't have to hire expensive American workers to produce in the US. It might make things with high capital cost much more affordable: imagine being able to 3D print out custom car body parts and have them assembled for the price of a high-end car. Impossible now.