He is not ready to "forgive and forget" and put "water under the bridge" for what he thinks those many did (or continue to do) to his country.
That's not a response to a "legitimate threat", but it's the expression of a legitimate (as far as that person is concerned) grievance.
You're aware of the meme going around regarding this phrase I assume? :)
No, I'm saying there can be an objective, reasoned aspect as to racism, that is doesn't have to be purely based on "fear".
We might be "very often ruled by emotion" but there's also an objective reality out there. A black guy flirting with a white woman in the 20's Alabama would indeed find themselves hanging from a tree -- whether they were "objective" or not.
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.
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.