Most psychologists are liberal because of academic orthodoxy,and its rigorous requirements. Psychologists in the public sector (VAs, academia) are far more liberal than private sector psychologists who deal with reality on a day-to-day basis.
I'm sorry, I should have been more precise. By "mental issues," I did not mean the many quirks of human behavior which fall within the range of what I consider "normal." (Many of which are listed in the DSM-whatever they're up to these days.) I was, rather, thinking of bona fide mental disorders.
I'm curious as to why academic orthodoxy and its rigorous requirements should cause a preponderance of liberals in the profession. My experience with true academic pursuit is that the necessary foundation in logic and rational thought precludes those who are incapable of that level of thought from participating. But then, I'm a scientist--which, at its purest, is an extremely literal and rational profession.
As for the large portion of liberals found in this study I would say it is more attributed to the suspicion of Psychology in the conservative sector..meaning..fewer conservatives see it as an viable science to study.
The science itself does not have an ideology, it is just a compilation of theories and tools about the workings of the mind and more recently the physiological workings of the brain.
Conservatives still have a flesh and blood brain..they just use it differently after years of maturity and experience. Many of the foundational studies and theories fall short because they focus on the younger years of development..even though as time has passed, we live decades longer. The science is still very much incomplete..like all other science.
I guess you have not been in academia for a while or you would recognize that logic as Eurocentric colonialist epistemology that has oppressed women and people of color for centuries. -sarc off