At least they picked them, and not worse. But I would have 'tackled' them.
On a walk around Rutland Water a few years back- I was admiring banks full of snowdrops- arriving by the car park, there was an elderly couple, butter wouldn't melt... who were digging dozens up, all organised with a box and trowel each. I politely told them to stop, as it is a nature reserve and the plants are there for all to enjoy and to multiply. They told me to mind my own business, and what was it to me anyhow. I told them again, quietly and politely to stop and they did not. I therefore phoned the ranger with my mobile who arrived minutes later- with other people clapping. They had to plant them all back- and he warned them it would be a heavy fine next time. Grrr. some people.
In our old village in East Leics, we had 1000s of daffodils on the verges, and it was awful to see many of them just snapped or trampled by some kids on way from school (: