alt Hacker News> Additionally some of these places would not have had the means to care for antiquities back in the day.
This is a bad argument, because it's irrelevant.
Imagine getting your car stolen, and the thief says it's justified because he is rich (partly due to stealing a lot of cars) and he can afford to send the car to the shop for maintenance more often.
The object belongs to the original owner. Even if that original owner would choose to destroy or damage their object on purpose that would be up to them.
I'm not very sympathetic with OP's positions, but I do think these analogies to individual theft are pretty weak. Who owns shared cultural artifacts? The government? The Ottoman government was in charge of Greece when they gave the Parthenon marbles to Lord Elgin. Was that stealing? If so, does the current Greek government have the authority to do what they want with them? And what's the difference? Both governments have supporters and detractors within Greece. There isn't nearly as clear of a distinction as most people want to think.