That's not the case with my family, at least. My mom was a green-card holder for almost 40 years until she finally got her citizenship a few years ago, and there was never any real hassle. She eventually got her citizenship mostly to simplify retirement planning (if she and my dad, who's a U.S.-born citizen, had different citizenships, apparently things get complicated with things like pensions and survivorship). I guess that's a kind of hassle, but a very cerebral one; she didn't get hassled at customs or anything, at least any more than I do. Probably being a middle-aged woman with an American family made her fit a low-risk profile anyway, but becoming a citizen has basically made no difference for her on that side of things.