It's a rather serious mistake to make--to claim that something is good or tolerable simply because it is natural. If it is inevitable that all of our minds will tend towards evil, that does not mean we should surrender to that tendency. Acknowledge, yes; surrender, never.

Nonetheless, outside of that error Derbyshire makes a lot of really good points. The final sentence of the letter is the most insightful. When we exclude those who practice group-exclusionism--when we cast people out as bigots, that doesn't necessarily decrease the prevalence of bigotry in the world. The danger is two fold--that reactance against such exclusion will promote bigotry, and that we new excluders ourselves will become new bigots.

And while all humans may tend to be groupist, it does seem that our groups tend to be growing wider--or at least fuzzier--as time goes on. The idea that group exclusionism is wrong wasn't invented by modern Political Correctness junkies or even by John Locke and Thomas Jefferson. You'll find that idea in a number of religions, both Abrahamiac and Dharmic. That idea is as old as civilization itself.