As an outsider looking in I see inherent problems with this discussion.
Firstly, there is a combined discussion about apples (plans) and oranges (kits). And there is a tendency to 'flip-flop' between the two when trying to make points, to support the argument.
Secondly, as pointed out by RAG, there is a big difference between running a company with overheads (premises and employees), and cottage industries (or paying hobby) where you are producing in an ad hoc manner or even knocking off other people's products.
In reality though, if you want to run a cottage industry legitimately you do need to consider overheads, and at some stage you will be big enough to have to pay tax and VAT, accountant and maybe employees. These would bump up your production costs, even as a cottage industry.