Regarding the current discourse over The Guardian and the word "queer"—it's a letter, in the opinion section, from a person unassociated with the newspaper. Stop acting like it's The Guardian's official stance on it.
Anyway, the person who wrote that letter is a big silly. 'Queer' has been used by LGBT+ advocacy groups for 30+ years already.
It's about as derogatory as calling something 'gay' is, which is to say, it's only an insult if the person who said it intended it to be.