Yes, it is shameful, but not uncommon! Our Tahoma National Cemetery, in Washington State has suffered damage of this type as well as thefts of National Colors from poles along the enterence. (Flags that were donated by people, with people buried there.)
The Korean War Memorial, in Olympia, WA was also trashed a couple of years ago.
I would have to guess that most of this type of thing is done by teenagers.