This is an interesting theory that relies on many assumptions, the probability of which is either unknown or at least not specified. For example the assumption of a generation being 25 years. To do a correct scientific analysis on this you would need to state the standard deviation of this age and carry the error bars forward into the calculation of each generation.
Secondly, the assumption of 4 children per family also requires a statement of the standard deviation. The error bars associated with this count also must be carried forward into any calculation of subsequent generations.
These are not the only assumptions that represent data that vary. Error bars on multiple variables, when carried forward into the calculation for the next generation interact with each other to grow the error bars on each subsequent generation. Then if you add in historical events such as plagues, floods, fires, wars, etc. you will need to make an assumption about how these events tended to decrease the population, and what effect this decrease had on the number of descendants in the affected generations.
My point is that with so many generations in between then and now, so many variables with unknown or at least unstated error bars, the figure of 67M descendants could be right for one set of assumptions.
With so many assumptions it is not possible to get an accurate count using only these data in the absence of an estimate of the probability that each assumption holds going forward into the next generation.
By the time you recursively carry forward a calculation with realistic error bars on each variable, the error bars on the calculated number may be so huge as to render the results be meaningless.
Given that this is the case, any conclusions drawn on these results also have the same degree of validity as the results on which they are based. Here again, more assumptions are required to carry forward the results into the conclusions.
This is not to discourage anyone from thinking about some of the points made in this essay. My point is that for some families, the essay will be more applicable than in others.
Birth, death and marriage records may not be available in all parts of the world. Records are destroyed in fires and storms. Some information is falsified to cover up dark and bloody family secrets. Hand-written records are transcribed incorrectly and lead to erroneous data in profiles.
We can't wait for perfect source data, approved by government agencies in "official records" to enter into profiles what we know to be true from family documents, such as the genealogy pages in family Bibles. Whereas not all family documents are 100% accurate, generally the inaccuracies will be about exact years of birth and death, not whether or not a person existed.
Given that the assumptions in this essay do not apply equally to all of my ancestors, I would answer the questions in the end of the essay as follows.
1. So are you really prepared for that responsibility? Answer: If not me than whom? Who else knows what I know or is willing to work on it? I wish that cousins would know more than I and would be willing to come forward. I don't like being the "family expert" because there is so much that I don't know.
2. Are you the only genealogist who has presumed to do so? Answer: No, but I am the only one who seems to be curious enough to ask the questions about certain generations in my family and the only one with sufficient time to spend on it. I wish more cousins more often would help to confirm or refute my work, or at least add to it, but everyone seems to have too much to do.
We can't be too afraid to make mistakes because this will discourage genealogists from doing anything that might be imperfect. If you make a mistake, just correct it and go on. (And don't forget to thank the kind WikiTreer who helped you find the error.)
3. And are you the best single one genealogist among them all, who is really prepared to accurately, or firstly, do so? Answer: This is an absurd question designed to discourage anyone new from trying to document what they know. We have no way to determine if we are the "best" genealogist because we can't be sure that there is no one better. Even if we could know who is best, do we really want him or her to be the only one to work on the family tree? All we can do is to identify someone who is better at it than we are. That will be the genealogist to whom we pose questions when we get confused. Then we must ask whether or not this better expert has the time to put into researching a particular branch of the family that interests us.
When appropriate, I will happily and thankfully defer to those with more experience and better knowledge that what I have. However, there is no way that they can know everything that I know.