I think any petition should be very careful and specific about its wording. The looting of antiquities causes enormous damage, and it is important to remember that while a private collection might preserve some historical information the process by which the antiquities got to that collection destroys far more. The retro-active application of any law is poor practice and wholly in-appropriate. However ultimately requiring collectors to in future follow due diligence is inevitable and a good thing, it should not be opposed.

Source: Personal knowledge.