He said all immigration is dangerous and should therefore be stopped. Are you getting this yet?
Your reading comprehension is atrocious. Let me make it simpler so you have a chance of understanding.
There was a time when many were coming to America, seeking a better life for them and their families. They worked hard, accepted American ideals, and assimilated into our society. This was the past condition.
Many people who want to come to America today share the goals of these past immigrants. It would be wonderful to be able to have them become American citizens to strengthen our great country. Unfortunately, the present reality is that there are bad actors whose goal is the destruction of America. Because it is impossible to determine who the bad actors are, or will be, the safety of American citizens must take precedence over the desires of non-Americans.
It is too bad that many good people would be denied the American opportunity because of the actions of a few. You remember when you were in school, throwing spit balls behind the teacher's back? The whole class got punished for your actions because they wouldn't give you up. It's just like that.
Hope this helps.