That's why I don't like enforced PvP in MUDs. PvP can add a lot to the game, but when you are weak and defenseless it just isn't fun to be killed by higher-levelled players over and over.
In Discworld (sorry, only MUD I know really well) PvP is optional. You can go PK once you feel you are ready, so you have plenty of time to prepare and make allies/enemies. No going back, though!
Some Guilds require you to be PK in order to advance past certain levels, but nothing stops you from advancing those skills on your own, or learning them from fellow players. This is true for the entire Assassin's Guild (as their main special skill involves "inhuming" players) and the Last Order of the Wizard's Guild.
What I also like about the Disc is the amount of races and classes.
There is 1 playable race, humans.
There are 6 Guilds with a few subdivisions each.
Each Guild gives you a set of commands unique to that Guild, but anyone can learn the skills from any guild and use many related commands. For example, anyone can learn to shoplift and steal, but only Thieves can learn to steal your undies while you're still wearing them.
Each guild has a few subdivisions which focus on specific skills, although you can still learn any other skills you like, just not as quickly.
Priests are the only ones where the subdivision really matters, as they each worship a different God with a different alignment and different rituals.
Other guilds besides Wizards and Witches can also worship gods as a follower so they can learn to cast a ritual or two, adding even more variety.
The result is that everyone clearly belongs to a certain group, but can still do almost anything they like.
XP and money can be a grind though, but you get xp for just being online, doing quests or entering areas you haven't been to in a while. Using any command also nets you XP, so casting toy spells or sneaking about for no good reason nets you xp as well. If you don't fight at all, but are an active player, you'll still get plenty of xp to advance your skills with. If you don't fight you won't need that xp for fighting skills anyways.