The reaction against immigration is a reaction to overpopulation, but the reaction could even be worse than the problem itself.

The reaction against immigration, in much of the world including USA, is like a symptom of a disease. The disease is over population, but the symptom could be worse than the disease, itself. It's like an auto immune disease where the reaction is worse than the disease itself.

The world could accommodate it's 8+ billion people better than it does today, but the reaction against new arrivals is pretty strong. The reaction indicates that there is a problem of too many people, but the reaction, itself, is likely worse than the actual problem.