So in your reality, we do not import tons upon tons of feedstuffs for livestock to the UK?My point is that if we in the west move to a plant based diet then that food has to be grown some place as the west can't grown all the food we eat or the range of food we want. Within the UK we have had to import food for over 300 years to meet our needs. This was amply proved in the last war when far more land was under the plough than before but we still had to import food. That food has to be grown some place and if a farmer in Africa will earn more growing mangetout than maze to feed his family a good diet they will grow mangetout.
You did not read the link did you, you just assumed it was all about the potato famine. At that time there was large scale famine all over Europe due to crop failure not just potatoes but other basic crops too. Ireland was just the worst case.
It's very relevant as it point out that if you rely on only one food group and disregard the rest the chances of famine are greatly increased. The often quoted, we can grow all we need on the land we have ignores the fact that most of that land is only suitable for growing a limited range of plants and in some case only one, grass. How much of Mongolia would grow rice, wheat, soyra or any other crop. Greenland, a vast area is unsuitable for growing but the fishing is good.
Veganism is a rich countries diet of choice and a poor countries diet of subsistence.