The tweet, possibly intended to capitalise on racial tensions, was in part inaccurate — there is no large-scale killing of farmers going on. But the part about land seizures is accurate.
The move is ostensibly about racial justice — white farmers own about 72 percent of the country's individually owned farmland, which they wouldn't own if not for colonialism and apartheid. The idea is to take some of that land and give it to black farmers. This is, naturally, a morally contentious issue — opponents will argue that since the current owners didn't do the seizing, they're entitled to compensation. But the policy is also about economics — South Africa's unemployment rate has been rising and now is more than 27 percent, a rate higher than anything suffered by the US during the depths of the Great Depression.
The government has been trying to put people to work by employing them in community and social services, but there's only so much that can do. Sending restless unemployed people out into the countryside to farm seems like an attractive alternative.
There are good reasons to believe that this might work — not only to absorb the country's surplus labour force, but to increase the country's agricultural output as well. The reason is a curious fact about farming that defies the trend for many other industries: negative economies of scale.
In most industries, bigger is better; a huge factory can usually produce cars or computer chips more efficiently than a small one, while a large national chain store can optimise its purchasing and logistics more efficiently than a mom-and-pop shop. In agriculture, that's also true in terms of overall productivity — a large mechanised farm doesn't use much labour, allowing it to produce lots of food cheaply. But small farms, especially in developing countries, tend to be more efficient in their use of land.