For instance, one experiment shows that frowning can have effects on your disposition. As an experiment, a subject is told to hold a pencil in their mouth in a certain way as to unknowingly produce a frown or smile and then do some task. The difference between behaviors is then attributed to smiling or frowning, as though the only thing going on with a pencil awkwardly in your mouth is the smiling or frowning.
Maybe I do view all psychology in a negative way but I imagine I find it distasteful the same way (I imagine) most people find the study of IQ differences among races distasteful. Is this a valid field of study? I don't know and I don't care to know because the racist overtones are so strong.
Unfortunately psychology, especially 'pop' psychology has been used to deny people their free will and restrict freedoms.
It goes along with an overall trend of the sciences to rely more and more on statistical methods which I find troubling.