Well, that and holding war crimes trials.
Context really is everything.
If you or I decided to disco dance in front of a Nazi death camp, we would deserve all the criticism that could be thrown at us, but this is a survivor of the Holocaust and his family, dancing to celebrate surviving Auschwitz. Some may see it as disrespectful, but if the people who died there could choose, I think they would prefer to be dancing. Further, I think it is entirely valid and appropriate to celebrate life in the face of so much death.
Obviously, grief, sadness and repugnance will always be a part of any visit to such a place of epic horror, but I don't think it is wrong for this man and his family to celebrate his survival. Some of the commenters accuse them of dancing on the graves of million of dead Jews, but I would look at it as dancing on the grave of the "Thousand Year Reich" that killed so many and tried, unsuccessfully, to kill him.
Remember, every time a Holocaust survivor or one of their descendants smiles, Hitler and his pals are forced to smoke another turd in Hell.
(crossposted from the Woodshed)