, while I agree about the lack of evidence, we must recognize that all scientific theories have parts without evidence to support it filling gaps with speculation when is needed. That's why there are people researching dark matter, in 1932 it was just a guess (not that is much different now but I'm not actualized); Piaget did a complete theory about human development describing the different stages, but when confronted with the driving force behind learning he hypothesized the "need to recover balance", a construct well behind the theories that describe the search for pleasure and the avoiding of displeasure, some of them well investigated by neurologist and behavioral psychologists.
A field with a lot of speculation is hypnosis, in the last conference I attended I saw the usual psychologists but also lots of medics and dentists that are using it in daily work, still there is a lot of speculation on what it is or why it works.
Science is a little group of facts and a lot of speculation, that conforms a way of thinking called paradigm, when a new explanation about a group of facts appears paradigm changes (not always, in social sciences they tend to coexist) but that new paradigm have a lot of speculation too. Speculation is what drives science growth.
BTW a book that I love about that is The Structure of Scientific Revolutions by Thomas Kuhn
, I think I will read it again this Christmas