You have to think longer term. UK unemployment was at 8.4% in 2012 - more than 1.3% above where SA is now. They didn't stopped skilled migration - or even cut general migration. The unemployment rate is now 5.4% - I think SA needs more young potential taxpayers who are educated at a high standard and have a lot to offer the economy in terms of skills and innovation.
Also, as a side issue; the amount of money these guys have paid into the system even before arriving is considerable.