Over on Tim Haines' Yahoo AncientArtifact list one may find a clear statement indicating that the collectors gathered there are not responsible:
Since the so-called Renfrew dictum was first voiced, the notion that looting is caused by private collecting of unprovenanced antiquities has gained a great deal of credence, becoming an article of faith for many archaeologists and others with an interest in archaeology, without their ever making individual in depth investigations as to whether this was really true. Because of my interest in understanding the intersection between collecting and cultural property law, I sought to determine the factual basis for this dictum, and found that nothing had ever been published that amounted to a scientifically valid proof, or even any real evidence tending to support such a conclusion. What has been published to date is instead much information regarding the extent of looting and illicit export/import of antiquities, and assertions to the effect that collectors are morally responsible for ascertaining the provenance of their acquisitions [regardless of whether it is practical to do so]. [...] The notion that looting is caused by private collecting of unprovenanced antiquities, so far as I can determine, is merely a perception, [...]
So there we have it. No need for collectors to feel at all responsible that all over the ancient world sites are being emptied by artefact hunters seeking collectables. There is "no scientific proof", it is all a mistaken perception and speculation and all the archaeologists and preservationists are wrong and the exploiters are right.
What about the explosion of looting on ancient sites in eastern Africa seeking collectable bits of terracotta figurines? The discovery of the Nok (and related) terracottas by western markets was the reason why sites in Nigeria, Burkina Faso and other countries were dug over to find them. How is no-questions-asked collecting "not responsible" there?
What about the denuding of surface sites in the Sahara of collectable artefacts such as stone beads, bracelets, and stone implements not due to collectors? They often buy them in bulk which are not even sourced to country, so totally decontextualised. How are collectors buying these things without asking where they come from "not responsible" for the continued denudal of these site?
All those temples in Southest Asia with their rows of decapitated statues, how are no-questions-asked collectors of exotic art "not responsible" there?
These are just three cases of many more where one can very safely interpret the evidence to support the postulate that no-questions-asked collecting has led to severe destruction of the cultural heritage by looters. The manner these collectors have chosen to acquire objects is responsible for the looting. In these cases there is no scientific evidence that collectors are "not responsible" for the looting. If AncientArtifact collectors wish to dispute that and provide scientific evidence that this looting was not a consequence of the collectiing of terracotta sculptures, Neolithic stone tools and "buddha" heads, then I am sure we would all be only too willing to hear it.
Over in the UK metal detectorists are busy emptying sites of collectable artefacts. That is what they are after, a new "hammie" or "Lizzie" or whatever to add to their collection (and that which they do not want can always be found a new home through eBay). The reason for this activity (artefact hunting) is collecting, most artefact hunters are artefact collectors, or they are doing it commercially for other collectors. Its not really a matterof seeking scientific prof that this is the case, one can go and talk to these people, see the stuff they have in their collections.
Over the other side of the Atlantic, those pot diggers rummaging around in 'Anasazi' pueblos and burial grounds are after collectable artefacts too. They are either collectors themselves, or are digging commercially to sell to people who are. Once again, it would be hard to challenge the postulate that (mere racially-inspired and other vandalism apart) the destruction of the archaeological heritage in regions where this occurs is driven by the desire of collectors to acquire dugup artefacts. There certainly is no scientific proof produced by the US "collectors' rights" lobby that no-questions-asked collectors are "not responsible" for the erosion and destruction of the archaeological record of the USA through artefact hunting.
In fact though this problem is closest to the US collectors and dealers arguing on Tim Haines' Yahoo discussion list and elsewhere that there is "no link" between what they themselves do and looting, no attempt is ever made by them to address the questions it raises about their own activities. It is here that we see the lie of the "no scientific proof" argument they haul out - it is not that the evidence is not there, it is just that a certain group of dealer-led collectors refuse to see it and think about it. Is that behaviour which can be regarded as "responsible"?
Vignette: Dugup Collectables.