Nigeria, June 15 -- Never poison a stream from which you may want to drink in future. That is a profound and timeless warning from the stable of our forebears. It is closely related to the modern idiom, "Don't burn your bridges."

In a literal sense, this proverb speaks directly to ecological and resource sustainability. If a community pollutes its local water source or overexploits its soil for short-term gain, it destroys its own long-term survival. In interpersonal relationships, ending friendships or romantic affairs with unnecessary malice, betrayal or acrimony destroys any hope of mutual respect or future reconciliation.

By violently attacking black African immigrants and forcing them to flee South Africa, the locals have sown a se...