Quantify those issues. At the scale of millions of people (I'm going to assume your 50 million was a typo, not that you're innumerate or gullible), one must qua

Quantify those issues. At the scale of millions of people (I'm going to assume your 50 million was a typo, not that you're innumerate or gullible), one must quantify. If 100 people out of 100,000 who migrate cause problems, and they are all fleeing intolerable living conditions, then the only reasonable way you can say that all 100,000 should be shut out is if you value the welfare of the 99,900 so low that it is outweighed by the social harm caused by the 100 even after taking into account the benefits of migration.