If you're on a PvE server, then they can't do anything to you, unless you flag yourself for PvP.
If you're on a PvP server, you're fair game when enter contested territories/enemy territories. If they're more than 5 levels above you, they gain literally nothing from killing you, but that really won't stop them from doing it on principal.
To be honest though, I leveled from 1-70 on a PvP server with my wife, and despite moments of frustration when we were being camped by someone multiple levels above us, it wasn't a terrible experience. In fact, we found that after transferring to a PvE server, we occasionally missed the joys of world PvP.
Additionally, there is plenty of content for the non-hardcore player. I would hardly say that my wife and I were hardcore - we just had time to waste on the game together, and as such we got to 80 pretty easily over the course of 2 expansions. Even so, we played a lot of alts, and between our less-than-maxed out level-capped characters and our alts, we never lacked for content to do things.
For the non-hardcore level-capped toon there's always daily quests, daily dungeons, and heroic instances. For the lower-level character it was pretty easy to find groups thanks to the new dungeon finder tool.
Bear in mind, however, that this is all based on pre-Cataclysm content. I can't say what, if anything, has changed since the newest expansion since we quit a few months before Cataclysm's release.