Please do not let the current controversy over mass illegal immigration and mass failure to enforce immigration laws blind you to this
poem's message: America is the world's dream.
There's an interesting literary technique in these verses. Bradbury begins in third person, speaking of "we" Americans, and later shifts to second person as he talks directly to "you" Americans.
Read the whole thing. And if the Mexican immigration fiasco gets you down, just imagine the leftist demonizers of Western civilization reacting to sentiments portraying Americans as "the hoped-for thing a hopeless world would be."