Powell saw immigration from Britain's former colonies leading to an upsurge of crime and poverty and the fragmentation of British society.
Legal immigration of South American and Central American Roman Catholics, of Eastern European Orthodox Christians, of Russian Jews, or of East Asian Confucianists, Buddhists, Shintoists, or Protestants (this last mostly from South Korea) even in numbers trebling the current quotas is not going to destroy America.
The same attitude against immigration met the Germans, the Irish, the Italians, the Greeks, the Poles. The notion that Mexicans, Guatemalans, Hondurans, or any of the other groups listed above (which I chose as they all show up in the 25% immigrant statistic for California), are somehow different is unsupportable.
Muslims, however, for obvious reasons drawn from the politicized, triumphalist and violence-prone nature of their 'revelation', are a different matter. Unless or until some sea-change in the dominant school of Koranic interpretation so that the verse of the sword is subordinated to the pacific suras, rather than the reverse, civilized nations have every reason to exclude Muslims.
When I first saw this I wondered what Colin Powell said about immigration. Then I realized it said 'Enoch' and not 'Eunuch'.