Sure, go ahead :) I agree that my answer wasn't particularly deep, but I have to say that I disagree with you if you think there is a singular answer to your question. Human desire is already too complex of a matter to deal with through one single perspective; that's kind of why I provided multiple answers, referring to the different fields of psychology as backdrops.

As for your second question, I like behavioral and social psychology a lot (alongside evolutionary, cognitive, cultural/community, personality, and developmental psychology in particular) but I'm much more interested in clinical psychology. I'm entering the clinical psychology program at university soon, actually.