In the first place you are talking about individual guilt, not collective guilt, for supposed receipt of stolen property. Moreover, not all of it is "knowing," since many landowners do not know even that they won land (if one owns shares in a REIT, for example), or about the wrongful appropriation of NA land (Don't underestimate the educational system's failures).
In the second place it is my understanding that some -- I don't know know much -- American land was voluntarily ceded by the Native Americans, not stolen outright, and not always on coercive terms. So whether every non-NA property owner is in receipt of stolen property is debatable at best; more likely, the situation varies with the particular circumstances.
Third, I find it how advocates of this general sort of position (that non-NA landowners own stolen property) go all Nozickean and anachronistically apply notions of private ownership of real estate that are Euro-American and (in my understanding) often have no NA counterparts, and (b) are the most extreme reactionary, right wing conceptions of private property that exist on the political map.
Certainly terrible crimes and moral wrongs were committed against the NAs in displacing them from the land, but wasn't part of the wrong precisely in privatizing it (or appropriating as government property with due compensation). At any rate there must be some better way of explaining what the wrong was than to apply notions of property and theft that would warm the heart of Robert Nozick, John Hospers, Richard Epstein -- not to mention George W. Bush, if he could understand them.
If we were to apply these right wing Euro-American notions to the situation, we'd probably have to say that, depending on the history, the NAs whose land the whites and Spanish appropriated was itself stolen. NAs had occupied the Americas for at least 10,000 years, and except for a handful of super-isolated groups, behaved like everyone else as a general rule in grabbing each other's land. So often the US Govt/White or Spanish settler appropriation of Indian land was theft. on this right wing account of what happened, from NAs who were thieves themselves.
If you are talking about the different fact that all privileged groups generally benefit from the disparities in power with oppressed groups, it does not seem to me that this is usefully discussed in terms of "collective guilt," or indeed guilty at all, which implies a certain sort of response to conscious wrongdoing, when the point is that in these cases there isn't conscious wrongdoing. My vehemently anti-racist 16 year old daughter is not morally equivalent to General Sheridan, even if she benefits from his crimes. That sort of talk is politically counterproductive too, because it just gets people's back up and alienates possible allies. The point isn't to make people feel bad about what they haven't done, but to get them outraged against the wrongs done to NA and other oppressed peoples, so that they might do something to help win those peoples justice.
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