Psychology is a science. Post about it in the science forum. It can also be a political topic, since politics involves a lot of *applied* social science. How to use these boards is: Figure out what you want to say, and figure out where that fits. A thread like, "psychology, discuss" is a really boring thread, but a thread like, "the psychology behind internet hookups," you could fit that in the hookups board, or the science board, depending on what the focus of your post is. A thread like "the psychology behind poor white people voting against their interests by voting republican" could go in the politics board.
I've noticed this trend of people asking for entire boards dedicated to like, every conceivable topic. It's not going to happen. It's not possible. The board list would be a mile long.