It's not just immigrants. I'm a citizen and am flying back from a two week trip to Japan today. One of the things that really stands out every time I make this trip is how pleasant, friendly, and helpful the Japanese customs and immigration agents are compared to the un-wiped ass wrinkles that are their American counterparts. I honestly think it is possible to assess those entering the U.S. without being a complete asshole during the process.
I travel internationally frequently and have never had trouble with US Customs. I think Argentina was the one I've had the most trouble with, and that was minor.
I travel internationally all the time as well, and my experience is that US immigration and customs treat people like suspects whereas their counterparts in Japan, and other countries I frequently visit, treat people like welcome guests.
