Ever found enough diamonds on a server to make a diamond block mansion and a full set of armor + tools, but then some idiot comes up and kills you before you can do so? I bet you'll say yes, its happened to me lots of times.
Almost every server you find allows the tormenting thievery that is PvP. That's why some person who has a heart and a brain should make a decent non PvP server!

~MinerPanda