Instead of thinking of them as scabs, how might it have beneficial for all unions to recruit immigrant groups in the union movement?

They would have added numbers--the large number of immigrants working for poor conditions could have added to the strength of the unions.

Immigrants could have added to the size of strikes and with them on the unions side, they would not have been working therefore strengthening the cause of the unions. Preventing them to join added to the division of the unions and undermined their cause until after World War I when immigration slowed. 

Yes, reasons why is sectionalism compromise of 1850 and secession i hope this

Im migration prohibition.