@thereisonlyoneofme
Depends on the definition of stolen. Some artefacts were legitimately acquired I think, i.e. elgin marbles? Could be wrong here. Greece has been asking for them back.
The Elgin marbles were absolutely not acquired legitimately, they were claimed to be have been give permission but evidence has never been found to prove this (despite similar documents been stored and recovered in some abundance). The Elgin marbles also received some of the worst restoration/preservation treatment of the period and have actually been permanently damaged because of it.
I trained as an archaeologist (BA MSc) and was working as one prior to covid. As an archaeologist this is something that's still very controversial. I've been to many museums, some like the BM and NHM that have artefacts and remains from across the world, some on temporary exhibits and some permanent. I'm still not certain where I stand, as mentioned above thread, there's some places where the past is actively been destroyed and efforts to preserve the sites are having little success due to the dangerous conditions and lack of funding. However, in the majority of cases there are absolutely reasons to return artefacts and remains as the infrastructure and legislation to protect them is there. There's very few good reasons for the Elgin marbles to remains in the UK when they were likely removed without permission and Greece actually wants them back and could tell the complete story rather than omitting the bits that makes Britain look bad.
The UK has some amazing heritage that is unfairly displayed in the big national museums because they can afford the associated costs around them. While there has been efforts to rebalance this (they now have to bid on the entire collection rather than the shiny bits, many also offer to local first) there's still problems with this.
So, I don't know where I stand, I love seeing cultural heritage from across the world when I visit the big museums and it would be a shame to not have the chance to see them in their countries of origin because I couldn't afford to travel but with technological advances and digital collections becoming more common then I can't see why they shouldn't be repatriated. They would fill the space with some amazing British heritage which no one knows much about yet (there's some amazing research going on right now across the UK).