It seems to me that the difference between "cultural preservationist" and "opportunistic pilferer" is largely about the motivation of the would be preservationist or pilferer. Do many question that these antiquities were need of preservation?
1. Consent is key in any excavations or artifact collection. Sometimes this will be through broad government-granted powers to specific organizations to rescue sites in immediate danger of destruction (i.e. rescue archaeology), but more commonly it's through permits to conduct research. You have a duty to find the stakeholders and ask permission.
2. You need to document provenance and minimize damage both to the site and collected artifacts. In many cases, leaving things in situ is the best way to preserve them. Most sites don't need to be excavated.
3. Artifacts need to be collected in accordance with ethical norms. That means things like no public photos of the deceased.
4. You don't ever sell anything you've collected. You're rescuing it or collecting it for scientific purposes. You don't own it.