I agree with many of the comment, but I think the saddest part of it is that, unless they really are committed facists, the chances are these are teenagers who did this 'for a laugh' and have no understanding whatsoever of the significance of what they have done.
Yes, it is awful, but if the Commonwealth War Graves Commission are responsible for the site you can be sure that the damage will be repaired very quickly.
They don't represent their whole generation though. For the teenagers who have been brought up without any knowledge or understanding of history and how they came to grow up in a free country, look at the increasing numbers of teenagers standing at the Menin Gate in the evenings, or those who stand in silence in Wootton Basset.
When I sell poppies in November it's hard to guess in advance. Sometimes it's the fresh faced smart youngsters who walk past and ignore me, whilst the Burberry badged trainer brigade come up and buy the poppies.
Rather than tar and feather, I'd prefer to see someone get through to them about what they have done - because once they understand, they will have to live with the knowledge.