Here are my problems with the phrase 'If you don't love it, leave':
1. To love something means you want what's best for it.
When someone says 'of you don't love it, leave', generally are saying want Australia to stay the same. They don't want to see new cultures, new ideas, new lifestyles, new communities. They hark back to a (possibly non-existent) time when things were more comfortable or predictable - a time when they felt more in control.
However, the phrase implies that they themselves actually love the place. Ironically, to properly love something often means trying to work towards improvements. To love Australia, by definition, means to want to see progress.
2. It assumes that everyone who doesn't love Australia must have been born elsewhere AND that they came here by choice.
One of the funny thing about migrants is that they have actually chosen to move to a place. Unlike people born into a country (like myself), they have made a conscious decision to come here. This implies that they may actually have a greater appreciation for all that the country has to offer, not less.
There are a second group of people from overseas, of course - refugees. These are people who haven't come to Australia by choice, per say. Its more that they were forced out of their country of origin by war, violence or persecution and who have managed to find safety in Australia (often with very little say in where the UNHCR will be able to place them). Of course, the level of gratefulness towards the Australian community and government among refugee groups is generally huge. And their desire to see Australia become more like their country of origin - the one that nearly had them killed - is pretty small.
Furthermore, there are plenty of people in Australia who were born here but who act in what our criminal codes describe as 'anti-social' ways. In other words, they are hardly acting as though they 'love' Australia.
The idea that all of these people should somehow go 'home' misses the last group of people and misunderstands the first two groups.
This one should be obvious. There are people who do not like the Australian community. But one of the
3. Many Australians have a false sense that just because they can get out their passport and buy a plane ticket to almost anywhere in the world, everyone can. 'Leave' isn't something everyone can do.
Lets dwell on the fact that, mostly, this phrase is used to talk about migrants and refugees. One of the tough things for parochial Australians to understand is that not everyone enjoys the benefit of being able to move around the world relatively unhindered. Sure, a few countries require a bit of pre-planning, but generally, if I have $5000 and a passport, I can go on a holiday at the drop of a hat. I can leave at pretty much any time - as long as I can make the airport before check in closes.
Most people from other countries can't do that. Their passports don't allow entry into many places and/or they don't have the means to simply pay for a plane ticket and go somewhere else. And that's true before we even look more specifically at refugees who, by definition, have no other place that they can legally and safely reside.
So, in summary, the very idea of the phrase is completely mad.