Researchers in the field of psychology can have any number of reasons to want to falsify their research. One of the leading motivators is the constant pressure to publish. In order to have a career in psychology, a psychologist must periodically publish their research and findings. In academics, "Publish or Perish" becomes the center of focus for scholars. In order to keep up in a competitive field, obtain funding for their research, or hope to obtain a tenure-track position, scholars are pressured to publish frequently. This harsh competitiveness is encouraged to further advance high-quality research, but more often than not results in low-quality and, in some cases, even falsified research being published in academic journals. Further pressure to publish comes from the need for funding. Imagine a frazzled professor, scrambling to get something published in time to acquire some much-needed funding, altering a few numbers to get the results they desire. This is sadly more common than professors would like to admit. With so many motivators in play, it is easy to see why so many psychologists would want or feel the need to fudge their results. Psychology is full of false research, making an indeterminate portion of its body of knowledge invalid. A field with such poor reliability can't be considered a real science.
Falsified research does not happen as often as it is made out. In fact, it probably happens just about as much as it would in any other scientific field. Peer-reviewed journals are also very discriminating about what they will and will not publish. The misguided actions of a few does not invalidate an entire body of knowledge, nor does it invalidate psychology as a science.
[P1] With the many pressures put on scholars and researchers to publish in peer-reviewed journals, the occurrence of falsifying research is alarmingly common. [P2] Psychology's body of knowledge is littered with false research which makes it unreliable. [P3] Psychology can't be considered a real science with such an unreliable body of knowledge.
Rejecting the premises
[Rejecting P1] Scholars falsifying research does not happen commonly. [Rejecting P2] Psychology's body of knowledge consists of carefully-researched content, statistics, and research. [Rejecting P3] A few dishonest scholars does not invalidate psychology as a science.