There is the analogy of you and your cat. Everything is fine as is. But suppose there is a switch, and you are the size of your cat, and the cat is now your size. How long do you think you will last?
Many of the immigrants, legal or otherwise, come from societies plagued with savage violence. In time, the immigrants will be the super majority, and savage violence will be the norm, not the exception. Happy future.
Like doubling the population of Chicago’s South Side.