Psychotherapy has been credited to Freud, but many, many others have come after him who have shaped it into the science it is today. Many of Freud's ideas were groundbreaking, but many of his ideas turned out to be wrong too. Psychology is a science because many have tested, proved or disproved others' theories.

Science has few "laws" (law of gravity!) --even ideas with loads of evidence need to be proven absolutely first. Psychology is ever changing to fit the latest research.