For those not convinced: every move that a union makes can be countered with an equal move on the part of the employer, and vice versa. Union makes an offer, employer has a counter-offer. Union strikes, employer locks them out. Union members have to live on strike pay (which is usually quite poor), employers watch their profits dry up. The only move an employer can make which union members have no equivalent move against is the hiring of scabs. The equivalent would be if unions could hire different managers who would pay them everything they're asking for. Since that's impossible, what, exactly, is the justification for scabs? It gives employers more power than the unions, which tips the scales inequitably against labour.
However, note that Kraft is also refusing to try to increase the workers' conditions to better than those already experienced in the country. That is, Kraft is trying to get away with giving a minimal level of benefits and pay. Now, at least one of the reasons offered for allowing multinationals to expand into other countries is that, by providing jobs, they help stimulate the economies and improve standards of living. Although this is only one example, it's a striking case of how inept this reasoning really is. Kraft has no intention of helping to improve South Africa's economy. Kraft is out to make as much money as possible, even if this means they must exploit vulnerable workers. That is, making as much money as possible is incompatible with improving standards of living. The two motives can, sometimes, co-exist, but will conflict. Which is why states need to choose which motive they wish to endorse: unfortunately, given what I have seen thus far, it seems that the South African government has endorsed profits over people.