Now, before you believe in wiki-haste that I'm just a nagging oddball, please note that my view is on the side of academics who have large issues with Starostin's work. There is no conspiracy against Starostin and his followers. We don't have a hate-on for him as a person and I'm sure he had a jovial spirit by all accounts, but these critiques arise because his theories are simply not tenable and too far-flung to be of use to a disciplined linguist. If people feel too personal about linguistic critiques, it's their issue to deal with.
"With fewer than 300 linguists in the world doing serious work on long-range comparisons, the discipline is small and perennially insecure about its scientific standards. Given the dearth of rigorous proof for some of Starostin's assertions, many American linguists felt within their rights to dismiss his research or at least to exclude him from their conferences and symposiums."
No matter. Starostin was unfazed and he set to work to create a hybrid language, more like a conlanger than a comparative linguist. He no doubt figured that his language would serve as a valid ancestor to both language families. Only one problem. It only works if you ignore rigourous methodology. Here are just a few flaws that I notice with North Caucasian that proponents just don't care enough about:
1. Violations of phonological markedness are everywhereThe number of protolanguages in his database and the wide variety is impressive. The quantity of seeming information alone would cause many to believe that his work is exceptional. However, quantity is not quality. I think that what the issue was with Sergei Starostin was that, like many language lovers, they failed to see that linguistics is a science and not a form of artistic expression.
I think Starostin had a "diacritic addiction". For example, all pronouns like first person *zō violate markedness because plain *z is so rare in his convoluted phonology while palatal *ź is used to explain almost everything (see his list of 'z words' here) where his diacritic bias is self-evident. Many phonemic exotica are far too often employed, such as *ƛ̣, to make up for his shortcomings in taking the time to adequately demonstrate sound correspondences (e.g. the ambiguous reconstruction *Ł_ĕɫV̆ with link here). Through the use of contrived sounds as a smokescreen, void of a discernible phonological structure that all human languages have, he can freely connect different etyma together no matter how large of a leapfrog we have to hurdle to swallow it, making it seem to laymen as though North Caucasian has a lot more evidence behind it than it actually does.
2. The pronominal system is unnatural
Considering that his reconstructed pronouns curiously use only voiced consonants, an attentive linguist might consider the effects of sentence-internal lenition on grammatical elements and more sensibly reconstruct unvoiced *s for *z in the 1ps pronoun or *t instead of *d for the 2ps pronoun. One might also reduce the bloated phonemic inventory to a more manageable level that could then be finally accounted for systematically by demonstrable proof, instead of leaving it all hanging as an empty assertion.
3. Shoddy claims in more understood language groups of his database compromise his credibility.
Nothing could be more far-flung than Altaic **séjra "three" (link here) when Altaicists reconstruct *göl- "three" on more direct evidence (Mongolian gurav, Japanese kokono-). Despite the fact that it is agreed upon by specialists that Proto-Dravidian is reconstructed without voicing contrast in stops (read here), Starostin took an anarchist approach by representing Dravidian with them (link here).