As must Darwinian evolution. While we can test and prove micro-evolution (adaptation and such), the same cannot be said for macro (one species to another). It is interesting how measuring rods are both dually convenient and inconvenient at the same time depending upon our preferences for what's being measure.
Macro vs micro evolution is a distinction made for convenience, not to represent any special difference between the two. Macro and micro evolution are the same thing on different time scales, and if one works, the other has to.
No, that's not necessarily true. That's an assumption, and one rather largely unproven. Thereby, it's not demonstrable and is therefore faith, not science.
That's the great thing about science -- using small things that we can observe to understand big things that we can't.
Your argument makes as much sense as saying that since we will probably never be able to watch a planet form up-close, we'll never understand how planet formation works. Who cares if we understand the basics (gravity, thermodynamics, radioactive decay, conservation of momentum), we haven't actually seen it so despite what we know, it must be magic.
For example, Newtonian Physics works great at the macro (every-day-object), slow-speed level. However, it substantially breaks down at the macro, high-speed and the micro levels. Einstein improved this with special relativity, though it still breaks down at the sub-micro levels, where Quantum mechanics fine tune from there using vastly different equations - different enough it cannot be reconciled (yet) with Newtonian and Einsteinian Physics. Yet, we wouldn't know that there is any break down of the Newtonian Physics without demonstrating it, the same goes for Einsteinian Physics.
Fact is, Macro Evolution has not been proven by any scientific means. Extrapolating it from Micro-Evolution is not valid science as it may not work or work any where near what we expect - which we won't know until we try to replicate it and succeed for fail.
Now for part of the kicker - Micro-Evolution has been shown to be temporary in many cases. Things "evolve" to meet a need, and as soon as the need is no longer they revert back. This has been shown time and time again - example: check out any of the examples used by Darwin to demonstrate Micro-Evolution; they all reverted after a time. All within his lifetime nonetheless.
Mutation, recombination, drift, selection... evolution.
We can observe the formation of new species in nature and the laboratory.
We have vast quantities of indirect evidence that the same mechanisms which produce speciation - the arising of new species - are the same mechanisms which, over longer timescales, lead to the development of new families, new orders, etc.
This claim that there is some sort of magical barrier which allows for so-called "microevolution" but prevents so-called "macroevolution" makes exactly as much sense as claiming that the forces of erosion can dissolve a sand castle, but that the "macroerosion" of mountains "has not been proven by any scientific means"... which is to say, no sense at all.
Never mind that science does not, ever, prove things true... it only disproves hypotheses, and those which are tested and not dis-proven are granted provisional validity, but always with the understanding that a new observation could result in the need to modify or discard old ideas which have passed past tests.
This pseudo-debate about "microevolution" vs. "macroevolution" is nothing more than an element of that propaganda campaign known as "Intelligent Design", the attempt to smuggle Creationism into the pubic school classroom and the public discussion by disguising its true intent behind a layer of pseudoscience. It has absolutely no scientific legitimacy.
