Why is migration bad?

Answer 1

Migration per se is not bad. It helps to create diversity and variety in a population and can inject skills and workers into a population that needs it (in developed countries with falling birth rates,migration helps to keep the number of workers high, which supports those that are economically inactive)

The problem comes with uncontroled migration, as these then outcompete native workers, particularly in low paid unskilled work. This breads resentment, particularly if it is concentrated in small areas.

Answer 2

Migration is bad because when you have a lot of people leaving one area for another, the section of the place is losing people. If you were to live in NYC nowadays, and there was a Great Migration, we'd be losing funds to help improve the cities condition. There'd be no more money to help support the schools and the utilities. There'd be no more sanitation department and etc.

In otherwords, you'd be losing money to help that place.

Shouldn't cost go down with fewer people? You are talking about what is sometimes called an "eroding tax base". You also failed to mention the flip side of this coin, mass movement means another location will have to stretch it's budget to support more people. People using mass transit, kids enrolled in schools those kids of things.