A griefer is a player in a multiplayer video game who deliberately irritates and harasses other players.
(See the history of the term greifing here)

You might say "Well, servers should have proper protection against griefers."

I'd say not necessarily, I think the players should be the ones thinking about what they are doing. It doesn't just frustrate the person who made the building/art/creation but the Server owner has to put up with an ugly destroyed building.

I don't see the point in greifing. It maybe funny but I see it as a different type of cyber-bullying/bullying.
A majority of servers don't allow griefing while most don't mainly the PvP servers allow it.

If it's allowed I don't see a problem with it but doing it when it's not allowed is really stupid.
Why can't people just follow the rules and have a good time that way?

Greifers - Think about it. What if someone was to grief your creations that took you time and effort? You wouldn't be too happy about it.

People that are victims of griefing - Just move on and build something else... If they continue to grief alert the server staff or move to a new server. Griefers tend to find it more fun when people scream with caps lock on in chat.

If you can't handle griefers I'd suggest a private server with a couple of trusted friends or play Single Player.

Since you have finished why not drop by my Facebook page and give it a like?