The "we took it to keep it safe" argument is kinda of weak, and still morally wrong
I suppose the nice thing to do in those situations would be to return those artifacts to the areas they came from once the place was reasonably stable, but in some situations that day has yet to come.
You may be right that the political situation has become complicated (the specific case of this obelisk is complicated) but let's not retroactively claim noble intent behind what at the time was little different than what the Vikings did when they showed up at Lindisfarne.
And yet they/we changed, and have preserved countless artifacts that even their original cultures are only now interested in. Not to forget that the very promotion of those foreign artifacts played a big role in making Westerners recognize the value of those other cultures and how much we have destroyed!
And as far as instability is concerned, a lot of that was caused by the same imperialist governments that looted the artifacts to begin with, so blaming those governments for that doesn't seem fair.
This is kind of where I stand on zoos. It sucks to see animals taken from their homes and held in unnatural captivity but the science, conservation, and educational aspects have a lot of value which is hard to ignore. A lot of people would never care if they didn't see with their own eyes what they stand to lose.
I have to admit I don't agree, I personally think the morality of a crime doesn't depend upon a value judgement of the of the victim. Theft is theft even if you steal from thieves, and two wrongs as they say don't make a right. But I suppose some people need to assume the victims of imperialism had it coming, but of course they themselves don't.
Good luck with that, and keep your doors locked.
That's not my point, no – if only because inter-personal relations are not and should not be handled like inter-state relations.
My point is that human history, especially in crucibles such as e.g. the Mediterranean is such a mess of victors turning to losers, conquerors to conquered, migrations, emigrations, remigrations, internal & external invasion, pillaging, destruction and so forth, that not only (i) the modern countries are all but representative of the people that inhabited them through History, (ii) so deeply intertwined, that trying to bring reparations is a lost cause from the very start.
Let us accept that the French should give back the obelisk: but then, to whom? To Turkey, the descendant country from the Ottoman Empire, who originally gifted it? To ethnic Mamluks, who controlled Egypt at the time as a client state of the Ottoman Empire? To Arabic people, ruled by Mamluks, who invaded Egypt before the Mamluks came into the picture? To Italian, Macedonians, or Greeks, that ruled over Egypt before that? Or should they launch some DNA sampling campaign to find what population in Norther Africa is the closest to the Ancient Egyptians, and bring back the Obelisk there?