If ambitious people in underdeveloped countries have no opportunities in their native country, they'll migrate to developed countries. If developed countries want to reduce migration, erecting border controls is not enough. There will still be ambitious people are still driven to improve themselves, and they'll cross borders illegally if that's what it takes.
So developed countries need to work with underdeveloped countries to create the conditions that will remove the need for the ambitious to be economic migrants, and instead gives them a chance of self-improvement in their homeland.
Take a look at this TED talk which describes a model to create cities that could perform this very function:
Free movement without borders is an end in itself for me, but to achieve this as a long term goal, the large numbers who fear large-scale immigration need to have their concerns addressed. Meanwhile, the government will only reduce net migration if it engaging in schemes like this.