The definition of griefing

[Rathrok]

Simply because it's not major damage doesn't make destruction of property permissible, the principle of it matters as well.
Besides, why did they need to destroy it to begin with?

it was two wooden fences, it was hardly a pain to replace. The harshest punishment anyone should have got for that was a warning and if the problem persists maybe a ban. And they needed to destroy it to gain access to a farm. my suspicions are that people are just using petty destruction acts as a way to try and hit back at people that have annoyed them, within server rules. like if they were robbed etc.