I have no scruples about elder flowers or berries, because like blackberries they're so copious, and because the vast majority of them grow far out of human reach -- I could take every spray of blossom from the few branches below head-height, and the rest of the tree would still be covered in it.

(In fact, come to think of it, elderberries don't seem to get eaten much; when picking them one has to take care not to select sprays where the berries have simply withered on the tree, rather than finding them already stripped by birds. A quick look on the Internet suggests that some people in the USA who grow them for fruit find that they need netting, while others report, like my own observations, that the fruit is more likely to drop off than get eaten.)