We do have borders, yes. We have an asylum process, we have an immigration process, we have a process for working permits, we have a naturalisation process, it’s all very well regulated and yes you can get through all of that without ever coming into contact with anyone in a uniform, short of a border guard.
What we don’t, and won’t, have is what you propose, and that is arresting American tourists on the subway for loudly speaking English. Or making it more difficult to open a Nigerian restaurant than a German one. That’s all your imagination, you’ve been told so multiple times by multiple people, and you still don’t seem to be able to understand it.