It does go both against practical politics - much of Europe was going through a population explosion and had neither room nor jobs for all those people - and against cherished beliefs. For one thing, people were much more terrifoied by Malthus than they were hopeful for a bright physiocratic future. Also, nineteenth-century Europeans may not have favoured freedom of foreigners to move to their countries, but they were in favour of freedom of movement in principle. Most states would simply have lacked the infrastructure to implement such a ban, and even though the purpose might not have been too controversial in principle, putting in place that kind of control mechanisms would have made people nervous in many places. Keep in mind, this is a time when North Germans routinely move to the Netherlands or Britain for a few years of paid employment before going home to start families, men from Schleswig-Holstein switch from Danes to Austrians to Prussians while captaining Dutch ships in the Indies, Belgians and Italians cross into France for seasonal labour, and Paris is crawling with German democrats and Russian anarchists. Border controls are - un-European, you might say. Despotic.
And I think the word for an Italy of 100 million people in 1900 would be "famine-ridden". The country had serious local food crises even with the safety valve of emigration.