When anyone rolls a new character on a PvP Realm, the game gives you fair warning of the consequences of doing so. That being said, if a player is out leveling their character, and a high level player swoops down and gank rapes the lowbie, is that okay? They were fairly warned BEFORE rolling on the server that things like that may happen.
Is it morally okay to gank like this? Do you give a fair pass to players who choose to gank lowbies for the "fun of it"? Personally, all my characters are on PvP realms. I think playing on a PvE server is a spineless way to play the game, and there is no war in the World of WARcraft. There is no anxiety that at any moment someone could swoop down from a flying mount and rape you. Thats the thrill you get when you play on a PvP server, and in the same token, its the risk you take.
Often, I will go on "gank sprees" as i like to call it, and find unsuspecting players and stalk them for a bit. Ill even let them know of my presence by /waving to them, /laughing at them, and /spitting on them, then ill proceed to mercilessly kill them, possibly several times to try to get them to bring a main or a guildie and start a PvP war. Its great fun, and I think its okay because of the stated rules by blizzard of a PvP server.