If that was true, it could happen towards any group and at all times, but it usually happens to specific groups in specific scenarios.

The anger and outrage helped keep blacks down, and thus their wages down, and keeping them for asking for more and competing with whites. Just like before the civil war it helped justify their being kept as slaves, and thus function as profit centers.

So it's not just irrational fear.

It's often the case that majority groups feel threatened by minority groups, or that the majority is jealous of a relatively more successful minority. Or that a minority group feels resentment for bad treatment.

These are all conditions that cause racial tension to flare. It's actually quite predictable, which reminds us that the spread of racism is like a social disease and should be treated as such.

coldtea was pointing out an example where racism is not irrational, but very rational indeed. It is statistically valid for black people in the US to be afraid of white people in certain situations.