The marbles were recognized as stolen at the time (ref: Britsh report of 1816).
So what? Any country that was looted deserved to have their heritage returned to them. I find it amusing that there was an outcry when the Taliban blew up ancient statues of Buddha, yet there is little or no outcry for the crimes the British have done it the past -- Lord Elgin's theft of the marbles, his burning down the Summer Palace of the Chinese Emperor etc, etc.
The British have promised the Greeks the return of the marbles since the mid 1800s. Even Tony Blair's government promised, and of course, has gone back on their promise.
I guess if the British loots and blows up another's heritage, its ok, if anyone else does it, its "bad"?
And if the British who previously made numerous promises to restore the marbles fail to do so, that's ok too, because after all they're British?