It took me a while, but I finally figured out why Evolutionists have problems with the teaching of Intelligent Design or Creationism in a science classroom: It's because they don't want people to point out that Evolution isn't a "science" so much as it is a philosophy.
See, Evolution is nothing more than a theorized (in a philosophical sense, not a scientific one) means by which everything living (in a biological sense) became what it is. In fact, the only scientific aspect of Evolution is the species adaptation (not species creation) aspects of biology. All of the species creation aspects cannot be proven for anything that already exists as its own species, since their creation cannot be replicated and observed under controlled conditions.
There have been claims that Evolution has been proven (in a scientific sense), when all that's really happened is that a given species has been proven to have the ability to adapt to its environment in a somewhat limited way. There are claims that the events in many religious texts cannot be proven by any scientific means, and therefore cannot be considered as falsifiable, and therefore aren't science-worthy subject. Yet Evolution has supposedly been given the blessing of the scientific community to be an actual scientific theory, even though it deals only with a possible explanation of assumed-historical events which have already been deemed impossible to actually prove through observation.
You see, you can't scientifically *prove* that history happened in a certain way because you can't actually observe it happening. You can certainly find evidence that *something* happened, but you can't, for instance, prove (in a scientific sense, i.e. through observation) that a specific, named person (one Sir Bubba Smith in England, let's say) in the 12th century sounded exactly like someone currently living (I don't know, maybe, Billie Piper from Dr. Who).
There's this emerging trend, when it comes to such issues, to intentionally obfuscate the language used, and to purposely use improper terminology in an attempt to confuse or otherwise intellectually disarm the person who holds a different viewpoint. The obfuscated language tends to come in the form of long, complex statements that use high-level terms that are really only used in a specific field of study as a form of shorthand. The improper terminology comes when words are intentionally chosen for their ability to confuse, for instance the seeming interchangeability of the words "evolution", "adaptation", and "mutation" and the claim that they all mean the same as "change" and are therefore all valid substitutions for each other (When this is done, I have to question the person's understanding of the language itself, because if I'm not mistaken, scientific method gets *very* specific in its wording since each denotes a completely different process, even if it gets a similar end result).
That methodology is strongly apparent in the kinds of arguments Evolutionists tend to like to bring forth, where you either need to actually be in the fields of study and intimately involved in such research to understand what they're saying, or they try to railroad you into a tangental argument and hope you aren't familiar enough with the subject that they can confuse you enough to get you to quit, or that they can keep you on tangents long enough for you to forget the original argument or the points you were planning on making and give up. With the former, if it can't be simplified into what most people would call "plain English", or it requires more than one or two graphs and a few paragraphs of text to explain, then they likely have no real contact with the real world beyond trying to bend it to fit their desires. If it's the latter, they really don't have much of a clue what they're trying to say, but they heard someone else say something that they can use as an argument (note: analogies will likely be used with impunity by these types).
I've actually been told that I don't understand how scientific theories come about or how they work, and I have to wonder if the people willing to make such a statement understand it themselves. As far as my high school science class taught me, a scientific theory had to be provable or disprovable through experimentation and observation. To say that Evolution is such a theory flies in the face of what the scientific method was taught to be as little as fifteen years ago in that it can't be provable without experimentation and observation, and any experiment would likely involve an intelligence (one or more scientists coming up with the experiment) and controlled conditions, both of which go against the idea of "natural evolution" and become more of an "intelligence-driven evolution" which is effectively that hated "Intelligent Design thing that those religious idiots keep trying to push".
Given that Creationism, I.D., and Evolution are attempting to describe a history, it cannot be proved or disproved through the scientific method as we have no way to observe the past in such a way as to confirm or deny each and every aspect in any of them. Just as we have no way to observe the creation of new, distinct species without applying an intelligence somewhere in the equation. We can't observe how a monkey became a human, or even how a virus (used due to the reproduction rate) became another, known and distinct virus (the e-coli experiment still only proved that e-coli can eat more than one kind of food, but it's still e-coli and can revert to its "natural" state given enough time).
Somehow, this relatively new philosophy became known as science, and was to be treated as fact until it could be proven false. When every other teaching in a science class must be at least tentatively shown to be true, this new theory needed no evidence to support it beyond conjecture. This all makes for an interestingly empty claim that faith has no place in a Science class, when it is only faith that serves as the foundation the Theory of Evolution rests on. Evolution was initially based entirely on the provision that there is no higher power, and that everything happened through pure chance and circumstance. This means that Creationism and Intelligent Design should be taught in the same classes and in the same ways that Evolution belongs: in a philosophy or comparative religion class, and not in a science class.