It'd be nice if the U.S. went through a few guilt rituals for slavery and Indian genocide. What you call guilt-tripping has kept Germany on pretty good behavior for the last 60 years.
[WS:] This has more to do with institutional de-nazification than guilt tripping - which almost always is as useful as the Catholic confession: it does little to stop future sins, it merely allows a moral redemption for the past ones.
Genocide at varying scale and level of success has occurred relatively frequent in human history - some of it recorded, some of it not. The more successful instances are probably unrecorded, as it is usually the victors who write and re-write history. This implies that attempts of one human group to wipe out, expel, or enslave another group is the norm rather than an exception.
Guilt tripping over selected instances of such attempts is counterproductive (assuming that the goal is to eliminate them altogether) for two reasons. First, it creates an impression of exceptionalism, which obscures the fact that no society is automatically virtuous in this respect, every single one is capable of doing it under the right set of conditions, as Richard Rubenstein (_The cunning of history_) aptly observed. Like a twelve-step programs that starts with the admission of "having a problem," eradication of genocide must start with recognition that it is not only "them" who can do it, but "us" as well.
Second, guild tripping is nothing more than modern equivalent of self-flagellation of the crusaders. It is a bogus response to a real problem, comparable to self-pity common among substance abusers. Its only effect is providing emotional comfort to the affected individuals, while doing nothing to address the roots of the problem.
So I am with Chris on this - to hell with guilt tripping.
Wojtek