My 2c:
Immigration is fundamentally a good thing. Yes, there are limits, but don't think the levels in Australia are unhealthy. Australia multicultural, 1/4 overseas born and 1/2 first generation, and we're right up the top as a rich, successful, free and fair country by world standards. That alone is overwhelming evidence.
Immigrants are more likely to be job creators. The type of person who leaves everything behind to move to a new country where they have fewer support networks is generally going to be more of a risk taker. More entrepreneurial, less welfare bum. They start small businesses, and this more than most things grows the economy. Even with all the talk of mining and automation, small businesses are the majority of the economy and the majority of the job market.
Personally, I think anyone who's got a reasonable degree from a reasonable university should be allowed in, no limits, and their immediate family (spouse, kids). And it's good for us - we get a free skilled person without the cost of a lifetime of state-subsidised education. I don't care if they can't speak English, they'll learn or adapt. Half the Italians and Greeks who came couldn't speak English either.
I don't agree with this concern about low-skills and automation. We've been automating for 100 years and outsourcing for 50. It comes in waves, we adapt, new professions are created to fill new specialisations, and we're better for it. There is no way to predict which big employer will go first. The best way to handle this technological progress is with an open mind to new ideas, which in practices means a diversity of cultural backgrounds. Jobs aren't a finite resource. The important thing is we have the safety nets so one small hic-up doesn't ruin someone's life, and the protections so people are paid and treated fairly (something we are losing focus on IMO).
Immigrants are good for trade. We trade so amazingly well with China because we are Chinese, we understand their culture, their way of doing business, so it's easier for us. Ditto all our big trading partners.
I don't agree with the arguments on infrastructure. That's a political failing, not a demographic one. There's plenty of examples of bad policy which has left us where we are: Howard's privatisation of everything, Carr's "Sydney is Full", subsidising private schools & hospital at the expense of public systems, a fear of debt, poor urban planning, pork barrelling, populism. We have the capacity to build and supply (or import) what we need to meet this demand, we lack the political ability. (House prices are a symptom of this IMO)
I don't think we should be telling where immigrants should live. They'll figure out where's best for them way better than any bureaucrat. The important thing is they be afforded the opportunities to be good little taxpayers, send their kids to school and be content.
I don't buy the Dick Smith argument that immigrants are bad for the environment - it's still a human wherever in the world it is. Australia has better environmental controls than most. That Australia has higher CO2 emissions than most countries, again, is a political failing we should be responding to regardless of immigration policy.
The caveat - they need support. They may even need welfare to start off with. Some may never succeed. But treat them as second class citizens and of course they'll fail. Give them a fair go. And remember it takes a generation, not an election cycle.