No one disputes that evolution happens, not even creationists
Actually, many of them do. Ken Ham is a great example of this, and despite being what most people would call a fringe lunatic, he still somehow manages to bilk millions of dollars out of his state government to promote his views, and achieve a stage to shout his views from in major media sources who want to pretend they're showing "balance" when covering evolution related discussions. It's him and people like him who are responsible for the Texas Board of Education's constant dumbing down of school science and biology textbooks, and constant attempts to force creationism into classrooms via poorly worded laws pretending to "teach the controversy".
Does all science really fall apart if we don't believe all life came from a single cell?
Actually, the idea that all life came from a single cell is pretty outdated, and was mostly never part of any serious scientific theory - any chemical reaction that would produce protocells (ie: the self-replicating molecules that would eventually become complex enough to call single-celled organisms) would have produced said protocells in the millions. I suspect that what you're really objecting to here is the idea that all life came from single-celled organisms, and no, science itself don't immediately fall apart if you don't accept that, just all of Biology, and a good chunk of the Chemistry that is based on biological processes. Astronomy and Physics for example, would be relatively unaffected by the complete loss of another discipline. The method by which you want to do this however, would have negative effects on all of science.
The reason you see so much about the importance of evolution being said by scientists is precisely because of the well funded fringe lunatics who are promoting the ID/Creationism view, and attempting to push it into schools, and push evolution out - they're doing it for religious reasons, not out of their claimed "value of seeing both sides". When you're presenting one side that has a literal mountain of evidence, proof, and useful predictions made from it, an alternative side that holds up a literalist interpretation of a translation of a translation of a series of stone-age parables is not an equivalent alternative explanation, regardless of how loudly the crazy person shouts. (And yes, Ken does claim that the modern english version of the bible that he uses is the perfect literal one, as do most of the others involved in forcing this idiocy into laws that are then struck down as unconstitutional and generally stupid.)
In short, scientists tell people about how important evolution is because they're defending themselves from nut-jobs who are trying to claim that it's all evil lies from the devil to corrupt our youths, and should be pushed out of schools. You wouldn't be hearing nearly so much about it if it wasn't for Ken and his fellow Creationists, and arguing that it should go away puts you into the same group as those people in the minds of anyone who has been watching the "debate", whether it's the ones on the side of reality who are tired of being attacked by crazy people and tend to get snappish at them after decades of defending themselves from unreasonable fanatics, or the Creationists themselves, who will count you in as they claim "See! Lots of people believe exactly the same as us!".
Going back to your original comment about not needing to know that a car was assembled by a robotic arm to know every detail of how it works, it's not quite an accurate comparison - taking evolution out of biology does in fact stop us from completely understanding how bodies and their internal parts work, as suddenly the commonalities between organisms that came from recent common ancestors have no reason for existing. Why does a squid work so differently from a fish, and why is the fish more similar to a human than it is to a fellow water-creature like the squid? The closer the common ancestor of a pair of creatures is, the more similar they will be internally. In your car example, it's more akin to saying "I don't need to know how an old Model T worked and is related to a modern Sports Car to understand everything about how the Sports Car works - we should just forget all that stuff about car designs having changed over time, they're unrelated." And yet when learning auto mechanics, how a basic internal combustion engine works is going to be taught long before they get into computer controlled fuel injection, and nobody gets angry at them for mentioning that those engines were the first ones, and others were developed from them later on.
Common descent isn't the basis for science upon which it rests, it's the resulting output of science being done honestly, and throwing it away is not only an insult to the people who have put all of their life's work into finding the answers to those questions, it would mean that the results of science don't matter and should just be casually tossed away whenever they make someone feel uncomfortable, thus meaning that if some cult out there decides that the world exists inside of a crystal sphere and the stars and planets are just painted on it, we'll all have to follow the precedent set by the disposal of evolution (to make creationists feel more comfortable) and get rid of any mention of the rest of the universe as actually existing. Evidence favors other stars and solar systems existing, but then it also favors evolution (in all of it's forms, including the bit about common descent) so if we're tossing one out the window for no valid reason, anything else is fair game as well.
(standard creationist attempt to deflect contrary evidence by making up crap about macro/micro evolution here)
There is no difference between macro and micro evolution, they're both evolution, predicted by the same theory, using the same mechanisms, producing the same effects, and both demonstrated very adequately. You can't have one without the other, because there's no separation between them except in the minds of creationists who are desperately trying to rationalize away evidence so that they don't have to admit their dogma is incorrect. Also, "macroevolution" has been demonstrated and documented quite clearly - take a look at your neighbor's dog. What breed is it? Do Toy Poodles or Dobermans look very much like Irish Setters? No? Do they act like them? No? Guess what, they come from the same original base stock, and successive mutations and selective breeding (ie: the same kind of selection Evolution describes, but in this case rather than starvation deciding who gets to breed, the owners and breeders act as the selective pressure) have lead to two completely different animals. Lots of other examples exist, such as the moths in the Black Forest of Germany, the entire fossil record, comparisons of DNA, and even examinations of various human populations in isolated regions of earth. Again, selective pressure resulting in physical change over time. The only reason there are more examples of evolution occurring in microorganisms is because the time between successive generations is on the order of days, hours, or even minutes, rather than years as it is in larger organisms. This does not mean it isn't happening, and definitely does not mean it hasn't been observed, it just means that setting up a lab to test it is not practical, because most institutions have this whole requirement that research result in publications during the lifetime of the researcher who set up the experiment.
As an aside, there is a difference between ID and creationism.
As for the difference between ID and Creationism, no ID doesn't know the limits of anything, it's just a dishonest re-branding of the same old garbage to try and sneak it past the "don't teach religion in our science classrooms" requirement. There was a whole big court case and media frenzy about this several years ago, and the judge agreed: ID _is_ creationism with a shiney new label glued on top of it, and all references to a christian god search-and-replaced with a more generic "creator" term. Still no science actually involved in it, just a lot of dishonest claims to the contrary.
Additionally, if there was no observation of the event and the process cannot be repeated, isn't it outside the realm of scientific discovery anyway?
Ah, I see what's wrong here - you're under the common mistaken belief that Evolutionary Theory says where life comes from. Sorry, it doesn't actually deal with that at all, it deals with what happens when there is already life present. Nothing more, nothing less. As for observations and processes being repeated, Evolution has been observed, and the processes have been repeated. That's why it counts as an actual Theory, while ID and Creationism do not, as they've never provided testable predictions.
So you believe in "God" but you think you have the wisdom to kill other people
You should check out the bible some time, it's full of things like orders from God to kill every last man, woman, child, all of their livestock, burn their belongings and salt their fields, and such. That whole "no killing" thing only applies to people who are part of the same tribe/religious sub-group in the actual original written form, and is frequently paraphrased and misquoted to say no to killing in general.
... you build missle launchers? You people blow me away.
I see what you did there.
UNIX was not designed to stop you from doing stupid things, because that would also stop you from doing clever things. -- Doug Gwyn