Darwin's theory of evolution is very threatening to fundamentalist Christians because it casts serious doubt on 2 basic tenets of Christianity:
1) That a god created all life forms as they currently appear (in evolution, all life evolved through natural processes)
2) That humans were created in their god's image - never sharing common ancestry with animals (in evolution, human share common ancestry with all living beings - at least on the surface of the earth, and including apes)
The problem of the theory of evolution for fundamentalists is that if these basic tenets are nothing more than allegory, humans aren't quite as important as they like to believe they are - and there might not be a creator - a god. To fundamentalists, this has to stop at all costs.
The basic tenet of intelligent design (ID) is that life forms are too complex to have evolved naturally. To explain, a concept called "irreducible complexity" supposes that some structures in life forms could not have evolved because if they were any less complex than they are, they would be useless. (This has been disproven numerous times.)
The societal issue with all of this is that although ID was proven in the Dover court case not to be a science and instead to be form of creationism repacked wiith new terminology, most people aren't aware of the case. So ID proponents (evangelical Christians) keep pushing the idea in "ever-evolving" ways - books, homeschool material, documentaries, websites... all with a very professional look (the megachurches have loads of money to pour into making them) and often by a fundamentalist Christian with an otherwise respectable college degree from a renowned institution. Therefore, as it reaches new and "virgin" audiences, they think "Hey, this is really good science."
For those who would like to stretch the idea of ID to meaning that life on earth could have been created by aliens from another world, this would not be in line with the ID creators wanted you to think, so they jump from saying there is an intelligent creator to the conclusion that this creator is the Judeo-Christian god. As far as any self-respecting scientist is concerned, even the thought that intelligent life on earth could have been created by aliens still leaves the question "then how did THEY come into being?"
1 - Watch the documentary "Judgment Day: Intelligent Design on Trial" - it'll answer many of your questions (including why fundamentalist Christians want to defund PBS).
2 - Know that there are emotional aspects of belief in the supernatural; psychology is a science, too, and also deserves exploration.
3 - Real scientist desire to know the truth - even if the truth bothers them emotionally, They don't think that because something is awe-provoking (or because they don't have all the answers), it must have involved supernatural intervention (see cartoon link below).