"Immigration enthusiasts are so hysterical"

This quote by Peter Brimelow recommends that those who favor immigration are overly emotional and irrational in their views. He implies that they are not looking at the issue objectively and are rather driven by their own feelings and enthusiasms. He might be implying that they are not considering the possible repercussions of migration, such as the financial and social impacts it can have on a country. He might likewise be suggesting that they are not taking a look at the concern from a legal viewpoint, and are rather counting on their own personal viewpoints. Ultimately, Brimelow is indicating that immigration enthusiasts are not taking a look at the problem in a well balanced and rational method.