Investigators Seek "Finders" in Arizona

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Pot hunters seeking items to sell to no-questions-asked collectors of such things are looting Arizona’s historic ruins at an alarming rate, according to archaeologists and investigators with the Tonto National Forest (Morgan Loew, 'Archaeologists Hunt Grave Robbers In AZ Backcountry', CBS 5 News November 4, 2010). Scott Wood, an archaeologist for the Tonto National Forest took a CBS 5 News team to the scene of one of the most recent lootings, a place called Mud Springs Ruins, inhabited by the Hohokam 700 years ago. This lies nearly 30 miles away from the nearest paved road, but even so had been plundered by artefact hunters.
At the centre of the 50-room complex were two freshly dug holes which seem to have been dug within the past six months. “What they’re looking for are the painted, decorated pottery -- the stuff that’s most often found, unfortunately, in graves in this area,” said Wood.

Law enforcement field officers work with archaeologists and investigators in the national park to discover who is responsible for the destruction of sites like this, but it is difficult to find clues months after the crime and it is proving impossible for state officials to guard every archaeological site in a region around the clock. It is believed that many of the finds from this sort of artefact hunting ends up on the black market: “It’s national. It’s international. Stuff stolen here can end up in the market in Europe, Saudi Arabia, Japan. There’s a market all over the world,” said Wood, who said that looting of sites like this in the United States tends to increase during economic downturns, which means more of America's historic sites remain at risk.

See the slide show accompanying the article.

This is what artefact hunters are doing (also illegally) in the "source countries" to seek artefacts to sell on the US market, but for some reason US collectors of ancient artefacts from other countries do not want to see the connection between what foreign diggers do and what the US diggers are doing to ancient sites in North America. They build a mental wall between the two and expect us to allow them to treat them as entirely separate phenomena, and get very resentful when we refuse to be taken in by that ploy. At least not until they explain in an articulate and logical manner where the two are different.

Why do US "collectors' rights" advocates only campaign to uphold US collectors' "rights" (sic) to collect items illegally taken from archaeological sites abroad, but never rise to the challenge to support US collectors' "rights" to collect whatever they fancy from US sites in the same way? What IS the difference?