Values Dissonance: Chesterton's racial and national attitudes were actually very moderate for the early twentieth century, but some (particularly in regards to the Jews) will often strike a sour note for modern readers in the midst of his most enjoyable works. This is mainly accidental, being connected less with racial theories (which he despised) than with a distrust of internationalism and big combines in general. His religious views, on the other hand, were entirely conscious, and will strike the reader as either refreshingly forthright or offensively aggressive. His opposition to progressivism, including essentially reactionary approaches to socialist welfare programs (such as government-mandated health insurance), science, and women's suffrage may irritate modern progressives, while his radical disdain for individualism, Realpolitik, nationalist expansionism, and capitalism may provoke modern conservatives.
Chesterton actually defended the Jews against the growing antisemitism in the West, in fact he was one of the few people who thought the Nazis were bad before WWII. Some of his reputation as an anti-Semite comes from confusion with his cousin, A K Chesterton, who was a fascist political activist and one of the most extreme Nazi-style conspiratorial anti-Semites among the British inter-war far right.
Chesterton was also called out folks behind the concept of Eugenics, even long before First World War. He even wrote about it in "Eugenics and other Evils"
One True Pairing: Chesterton once wrote an essay regarding Don Juan of Austria (no relation to the famous lover of the same name) and Mary Queen of Scots. His focus was not particularly on the "bohemian" details of their romance but on the fittingness of such a pairing and the historical-political implications across time.