Why did both supporters and opponents of immigration quotas believe they were defending American traditions and values?

The idea of immigration quotas generated much heat among Americans, some supported the idea while others were completely against it. The Americans who supported the idea of immigration quotas believed that America is a land of immigrants and foreigners should be allowed to move into the country in order to enrich diversity in the country. The opponents on the other hands believed that immigrants, with their diverse cultures, religions and traditions will have negative impacts on America. Besides, they believe that allowing these people into America will cause unemployment.