Psychiatry has it's problems - but so does every other area of medicine. Psychiatry is at least based on science even if it does deal with certain aspects of human behavior etc that have not been full quantified yet.
Scientology on the other hand is basically a science fiction novel converted to a for profit religion. There really isn't much of a comparison here. While psychiatry may still have many unanswered questions it isn't a collection of thoughts pulled from the
assimagination of some random guy.