Earlier quoted context omitted.
It's unjust, particularly because "being a Nigerian in Nigeria" is not a condition that most people in that condition can simply elect to remove themselves from. Consider the situation from a Rawlsian veil of ignorance perspective.
Try explaining that perspective to your spouse after you lose money in a 419 scam. "But honey, I didn't know that this Nigerian was a con-artist. I had to give him a chance!"
That's not to say it may not be effective, on average, in limiting losses. But effectiveness is something distinct from fairness.