What are Advantages and disadvantages of quota system?

The arguments for the quota system are that new immigrants are a threat to the future, New immigrants are difficult to integrate, little land remains for immigrants, American society will be strained by clashes of cultures.

Againtst quota system would be that immigrants are not a threat, The languege barrier does not imply menta inferiority, They will be lured by the oppurtunity in America and will work hard.