As opening lines in letters go, "I find you deeply offensive", is pretty direct. Fair enough. I suspect lots of people do. It's a natural consequence of media work. But then my anonymous correspondent decided to explain why: "You are foreign, you shall always be so. Piss off back to whatever Middle Eastern sinkhole you blew in here from."

There's nothing surprising about this. There's nothing even particularly rare about it. Some version of that letter arrives every few months. This one was particularly unvarnished – complete with references to my wife and "half-caste kids" and cheerful threats of the return of the White Australia Policy – but the message hardly varies: this isn't my country and my public presence is unwelcome, either because I'm a Muslim, or because in some racially determinable way not a "real" Australian. I've been accused of everything from taking elocution lessons to changing the spelling of my name to appear deceptively Australian before I unleash some Trojan conspiracy. Apparently, Aly is roughly equivalent to Smith. They're onto me.

I have almost no emotional reaction to this kind of goonish racism. It's simply too ridiculous to engage me. In fact, I'd completely forgotten about this most recent letter until racist ranting hit the headlines this week following yet another racist diatribe on a Sydney bus that was captured and posted to YouTube. It's at least the third such case in about four months. Hence the fresh round of debate on Australian racism that always seems to follow the same unedifying pattern.

First comes the shock, as though such incidents reveal something we never knew existed. Then comes the argument over whether or not Australia is a racist country. Frankly, I don't know what the argument means. Every country has racism. How much do you need before a country itself is racist? Is it a matter of essence or degree? Do we judge it by surveying legislation, newspapers or behaviour on public transport? And even if we can answer those questions, then what?