I don't mind people using Dark Magic, as it's still avoidable if you're quick enough. I do despise people who aren't honourable to fight against though, either because they attack me while I'm bowing, or have deliberately kept their level low while becoming overpowered. I've done that for a one shot boss challenge, and while still SL1 I had a fully upgraded Pyromancy Flame and every spell, and I could have beasted anyone if I invaded them, but I didn't. Hopefully in DS2 they'll figure out some way to make sure that the people who can invade you are of a more similar level equipment wise as well as Soul Level wise.