Opponents attempt to scare the American people with tales of immigrants committing crimes and taking welfare. The culture of the immigrants is said to be a threat to American culture. These are red herrings. If the government didn't tax productive American people to provide welfare, no one could go on the dole. As for the culture, it is robust precisely because it is open and spontaneous.
Immigration enriches American culture.
The concern about culture reminds me of the concern about the future of the English language. There is no danger of English's going into decline. The policy debate, mired as it is in welfare, education, and labor statistics, misses the key points. First, the freedom to move about peacefully is a natural right. That is not to say there is a right to trespass.