What is the mechanism that prevents microevolution to become macroevolution?

You ask if speciation means less genetic diversity. I have two answers, not necessarily and probably. You have to keep the proper frame of reference.We start with a specific amount of genetic material within a population; As the population speciates, the genetic information gets divided up amongst the various isolated populations. Of course there's a lot of redundancy; that's why speciation is normally a slow process. Let's suppose we have a species that possesses 30,000 genes. Two populations form from this species that become geographically isolated. Originally, there's a lot of genetic redundancy (or overlap). So let's suppose that of the original 30,000 genes, all the alleles are present for 29,990 genes. But for a small number of genes (10 in this case) there is geographic isolation, no overlap between populations. This occurs purely by chance, remember. So, is there a reduction of genetic diversity? Not really, the sum population still possesses the full diversity of alleles among its 30,000 genes. However there has been a reduction of genetic diversity as seen in each population.Now, time adds up; This process repeats itself, until specific alleles become so poorly represented in a suficiently small population that they are in danger of being lost, should that population cease to be. In fact this is what happens, resulting in a true loss of genetic
diversity, both from the over-arching population view and as seen on the small population or individual level..An infinte amount of species (as you brought up) would not necessarily be equated with a loss of diversity, but it likely would because of the afore-mentioned factors..

What does "common sense" have to do with anything? To you common sense is clearly something different than to me.I gave you the explanation of speciation that almost every biologist would agree with. How that beomes "irrational fanaticism" i'm not too sure.But tell me more about this "common sense" criteria...How does it work? I mean, when I observe that there exist many separate populations of say, finche, common sense doesn't really tell me much about the underlying genetic situation. I have to study it, to find out what's really going on. Common sense doesn't tell me anything. A clear mis-representation of what I said. How is it usually phrased here? A Strawman?
We're talking about a loss of genetic diversity - ie genetic information. Every subsequent speciation leads to less genetic information than before. No, it does not; My model does not consider mutations to be a source of information great enough to overcome the loss of information due to speciation. Never does it assume the non-existence of mutations (good, bad, or neutral). This means: IF mutations increase genetic information/diversity, they have never been demonstrated (nor do any biologist hold to such a theory, that I know of) to overcome the loss caused by speciation. The Net Change then is negative. I'm not sure how this fits in..