Many of those Nigerians are thugs and bring it on themselves. But there are a lot of others - eg Zambians, Zimbabweans, Ethiopians and Somalis- who risk life and limb every time an outbreak of xenophobia breaks out
The RSA military used to be posted at the borders, to keep them out/catch them if they made it and return them home; though thruth be told, some did manage to get in and stay. Sadly, that more or less stopped a while back and so, there's very good reason for RSA blacks's not wanting them there!