I can go to Sweden (and thus the entire Schengen zone, i.e. most of Western Europe) with just a passport, no visa. Why is the reverse not true? Europe is just as popular a destination as the States. Is there a flood of Swedes trying to illegaly immigrate?

"Unity" and "culture" don't "make America great". (Nor does the US even have a single culture. There are dozens within a mile radius of where I sit.) Greatness is only bestowed by others, and, non-Americans have really started looking down on America thanks to its antagonistic travel policies that strain friendships, families, and business ties.