Again, you're not 'wrong' but the economics are not that simple. They once were... maybe still are in some places. But in the developed world, the economic model of industrialised animal farming is now getting weird. There is not such a direct line between the volume of meat produced (the primary commodity) and the viability of the business. You are saying that the value of the meat is primary because you couldn't derive sufficient value from the rest, but in Europe where I live, you usually can't derive sufficient value from all the products together! The industry is heavily subsidised, and the viability to farmers and to agrobusinesses relies on taxpayer subsidies paid per head of cattle, or per unit of land. So to the farmer/business selling the cow, its market value can't really be reduced to one product, even if it's the product with the biggest value. That's what I mean when I say that nothing is a byproduct. Every part that is paid for (including the subsidies) contributes to putting the business in the red or the black. If a quirk of the market meant that the most valuable part of the cow was, briefly, the gall bladder from which a powerful new anti-cancer drug was derived, vegans would probably not decide that meat was therefore a secondary 'byproduct' that was ethical to consume.