As one who is trained in mathematical research, I know that a theory must begin with some assumptions that are not subject to proof. Changing these assumptions will yield different conclusions. For example, the assumptions of Euclidean (or Newtonian) geometry yield "flat" space. This was the prevailing notion of the universe until Einstein used different assumptions and derived a "curved" space-time.
Similarly, a scientific theory starts with some assumptions (often framed in mathematical terms) which are not capable of direct proof. No theory can come out of zero assumptions. The crucial difference between mathematics and science is that mathematicians are happy to study and allow various competing "theoretical" models to flourish in their minds whereas scientists must view each theory through the lens of reality to determine which accords with the real world.
Deciding which scientific theory to accept or reject should be straightforward. It should be purely a matter of whether the observations agree with the conclusions. Unfortunately scientists in the scientific establishment have taken upon themselves to decide which assumptions are permissible and which are not (ie, "non-scientific").
In the matter of the origin of the universe (and the development of living organisms), some scientists have succumbed to their own religious (or, rather, anti-religious) preferences by tacitly incorporating an assumption (unprovable) that there is no intelligent designer (or God).
With their postmodern bias of unbelief, such scientists have ceased to be open enquirers of the truth. They oppose the teaching of Intelligent Design Theory, proclaiming it to be non-scientific and unverifiable. Surely, science should be verifying whether the conclusions of the theory fit the facts. You don't try to verify the postulates directly.
Has anyone actually seen a postulated nuclear particle with his own eyes? Is it a round ball? Yet these occasionally squeamish scientists insist that we cannot postulate an "Intelligent Designer". They'll probably demand that this postulated Designer appear in front of them but even then; they may still claim it's an illusion!
In accordance with Charles Darwin, establishment scientists see no fundamental distinction between macro-evolution and micro-evolution. The former is disputed by many scientists though the latter is accepted by most. Gregor Mendel, known as the "father of modern genetics", rejected macro-evolution. I'm not discounting all of evolutionary theory but specifically macro-evolution including that which links man to the primates.
Many counter-arguments to macro-evolution have been developed by various scientists, for example those based on observations indicating a loss of genetic information rather than greater diversity. A recent discovery of a cell's ability to recover correct genetic information despite parents with flawed genes also casts doubts on evolution theory.
Scientists are presumed to be open-minded yet though macro-evolution is still unsubstantiated they pronounce it as the established truth and presume to bar all teaching of alternative theories from the classroom. This is not free enquiry but an imposition of their postmodern ethos that there is no God, no spirit realm, and only the material world exists.
They discount, a priori, any possibility that a spiritual being can manifest itself through empirically verifiable activities in the material realm. Some people testify to being healed of terminal cancers; their doctors have no explanation, and yet the scientists, under an a priori assumption that there is no God, excludes the possibility of miracles (either an accelerated operation of the scientific laws or their suspension).
A good scientist must be open-minded, open to every possibility. In the evaluation of the theories of intelligent design vs. macro-evolution, postmodern scientists have, by and large, failed this test. Indeed, by stipulating what can be a scientific assumption and what cannot be one, they are playing God.
As one who believes that the universe is not an accident (the probabilities weigh against it), I believe it is a matter of time before macro-evolution will be nailed down in the coffin by an ever-increasing preponderance of evidences now trickling in. Some might prefer to wait all night for the sun to rise but do we have that much time before we believe?