You'd better believe it happens everywhere. There are dickheads anywhere - when you've got 15,000 humans in one place, there's simply bound to be.
One thing to consider in all this, of course, is that Australian grounds are generally bigger than most, and hence there is often larger audiences and therefore more potential for the small dickhead population to rear its ugly head.
It's exactly the same as someone not wanting to go to watch a game in Kolkata because of fear of riots. Yeah, it's not exactly likely, but if you get caught up in something that does happen - you'd best prepare for one of the worst things anyone could wish to experience.
Just like you'd be a fool to judge most Indians by the few that riot at the occasional cricket-match, you'd be a fool to judge most Australians by the few that throw racist bull**** around. Nonetheless, the fact that something like that is a possibility that cannot be ruled-out could quite easily put a rational and sensible person off going to a ground in a place where that's possible.
Of course, here in the UK we never have any problems at cricket.
We're saintly holier-than-thous.
And yet as recently as
1992 there were some of the most disgraceful scenes you could ever wish to see at a cricket match, as Pakistani contingents were subjected to not merely racial taunts, but a pig's head being thrown into their seating area.