I understand what you're saying Will, but I do think apologizing is important, even if it can't be 100 % sincere.
It is perhaps a little different in the case of Native Americans and the US, because the US is still benefiting from what it took from the Indians, and does not intend to return more land.
So all you could do is apologize for the brutality with which the lands were taken, which sounds rather weak.
In Europe the colonies have become independent, and we could apologize to the new nations.
We benefited from colonialism at the time, and we wouldn't be giving back the wealth we took (we spent most of it fighting other Europeans in WWI anyway) but we could state that we recognize that the principles
we used to justify our behaviour were all wrong: that we had no right, because we were European, white, Christian and mighty, to take what was there for the grabbing.
Grabbing is human, yes, but this is why we have laws, to hold our general impulses for grabbing in check. That's why we have the United Nations.
If people stop grabbing (at least some of the time!) because they are afraid of the police, it's not as worthy as if they behaved virtuously of their own accord, but it's still acceptable.
Also apologizing in Europe would be a sort of damage control: if we go on putting the inept sentences quoted from Belgium in our school books, how will the wounds between Africa and Europe, and between us and our immigrants, ever heal?
They will recognize our apologies for what they are: unsatisfactory and incomplete, but it would be a start.