If someone is to get a legal permit or has bought the items then I think it is alright to have the makers concent, however for the items to be excuvated from the home country and then bought over is not acceptable and they should be retured from thier rightful owners.
It has been shown that if artifacts are not stored in a safe, temperate container, sunlight, heat, and humidity will destroy them. Pests like termites will eat away at them, and people will have the opportunity to steal or vandalize them. Also, historical artifacts belong to everyone! People should not have to pay huge sums of money to travel around the world to see these artifacts. Keeping at least some artifacts in different museums will allow millions of people to see them every year!
Yes. In times of war or civil unrest, it is important to ensure the history of the respective country's culture is protected. In many cases, items can be returned once the difficult period is over. In cases where there is long term unrest, the items should be protected at a museum in a safe location for the rest of the world to enjoy.
No, it is not unjustified in every case to remove artifacts in order to preserve them from destruction, because sometimes the home country is not capable of preserving them. A country does not have a claim to the artificat just because for whatever reason it happened to be in their country first. If another country owns it, they are capable of preserve it, and in most cases, they do a fine job.