In monopolized markets P>MC so utility is not maximized. That means that resources that are used in the monopolized market could have alternate uses in a perfectly competitive market that would lead to a greater consumer's surplus and greater utility. That's why monopolies are inefficient from society's viewpoint.
About the Author: Mike Fladien is a high school Economics and Law teacher in Muscatine, Iowa. He has been called the EconHacker because he has a talent for explaining Economics concepts in a simple language that anyone can understand.