Me: "The problem is calculating the orbital period of Jupiter."
Someone: "Here's the orbital period of Saturn."
Me: "That wasn't the question."
You: "Yeah those goalposts just keep moving."
No there are no moving goalposts, just people not bothering to actually read and understand the point they're responding to before responding. The point that started this tangent is and has always been that if people stop eating beef but not stop consuming dairy products this would still drastically reduce the cow population because these are not the same animals and the fact that dairy cows are also beef cows (ie the set of dairy cows is a subset of the set of beef cows) does not make these sets the same, it merely makes one a subset of the other.
What error?
I highly doubt it. It doesn't take an agricultural expert to realize that farmers would not raise beef herds if nobody ate beef, and the fact that cows in those beef herds produce milk for their own calves does not change this, as that milk does not provide income for the farmer - for that it would have to be sold rather than just consumed by the cows' own calves.