Griefing unclaimed territory is
allowed, since it's the player's fault for not claiming their land.
However, stealing, raiding, or griefing a claimed area is
not allowed. This is
peaceful survival. If you want to grief and raid people,
go play factions. People don't want to deal with having to be stingy with who they're adding to their party because theft is allowed. They don't want to have to wonder, "Is this person going to break my stuff," because they want to play with more than just themselves. It's common sense really. Either go play Factions, or go play Anarchy if you want to grief. 99% of Survival servers that are large don't allow griefing.
You can view the network rules
here. Scroll down to the Survival section.
Cheers.