You have a point. You could find someones profile by entering their username or their ID but that's impractical. After thinking about it, ultimately it doesn't

You have a point. You could find someones profile by entering their username or their ID but that's impractical. After thinking about it, ultimately it doesn't make a lot of sense; if you have a Facebook account, you should be able to find people using friends-of-friends or by other means. I guess the primary use-case is to help prevent cyberbullying?