Immigration reminds me a lot of the NIMBYs. Yes, we want immigration, but only those who are exactly like us and do exactly the jobs that we don't want to do, or he ones we can't fill. The rest will only try to change our culture with their culture.
I just made the economic argument for migration in a post that Azircon wrote, about Japan. Migration is very similar to food - we have enough people (and talent) on earth to fill all open positions, but it's the distribution that doesn't work, just like we could feed the world easily. As long as the negative impact on an economy is not big enough, the rules won't change. It would be smarter to start early on, create a educational system that is adapted to challenges posed by an immigrant population, and in one or two generations there would be a good workforce to keep funding the social system. But that requires forward thinking, and quite a bit of effort - most countries wait until the roof is burning.
Which is why they are creating robots for it. But, they too will change culture. They already are.
Most people too. We keep voting for the people who promise to solve our immediate problems and every few years, we choose more when they failed.