Some see immigration as a negative phenomenon, as it affects economy, jobs and rights of native people. While other see immigration as a good thing because it can bring new consumers, new culture, new knowledge. It is always possible to point out advantages and disadvantages.
Immigration is a natural human phenomenon, but modern societies with civil rights evolutions are addressing it differently than earlier as now there is so much more control over borders and passages of humans from one place to another.
The positive side it can help grow the economy, regulate and increase low birth rate or problems with elderly populations, fill up jobs or positions that are out of the market in certain place (example: for lower and heavy jobs or either high skilled as nurses or doctors). The negative side is if there is no job for the immigrants or houses enough they will be homeless and will need support from the government, this can affect negative all the social structure, bringing health issues, increase of violence and many other issues.