You make some pretty big assumptions here that, when tested, have always shown to be partial truths. Nations with the lowest net immigration and lowest steady population growth have significantly higher standards of living, less social unrest and generally healthier societies.
Check out Hans Roslings TED work or go to Gap minder and run the simulations yourself. the question of needing more people for a health economy is a false one. More spending is what will drive an economy, and it has always shown to better is less people have more money and spend more, rather than more people spending individually smaller amounts.
It's basically just that the population argument has been hijacked and all opposing points of view, especially regarding limiting population growth, are quickly crushed.
Check out Dick Smiths' population puzzle.
So how do you stop a country's culture being eroded. It is pretty simple really, strong effective governments who are not afraid to say what has to be said and do what has to be done, even if it means selective immigration in terms of education levels or whatever, or imposing strict immediate return policies should things not work out.
Sure Putin is a tool, but his words are kind of interesting on this point: Minorities need Russia more than Russia needs minorities.
We just need leadership with spine and good clear out of all the bleeding heart, perpetually up in arms, serially offended, uber liberals from media.
