I think I would quit and never come back if arctic added a nopkill switch option.
Honestly, I rarely ever pkill anymore, I don't believe I have attacked another player intentionally in the last 3 years, but a huge part of the enjoyment of the game is the knowledge and fear that I could be attacked at any moment by a fellow player. Having an "opt pkill" that makes me invulnerable to player attacks would destroy that feel and make the game just a lame PvE grind.
OTOH, there have been various times in arctic's history where pkilling was de-incentivized, even if it was totally allowed. If done well, I don't have a problem with a change along these lines, and it could really spice up the game in a positive way. This is based on my memory, I might be getting a few details wrong:
1997 era: you were penalized if you attacked and killed a player of lower level. Back during this time, I actually engaged in pkilling, because it was doable at lower levels and I was a newbie and it seemed like killing someone's twinked out alt for gear was a lot easier than actually doing zones to collect gear. So I'd have a level 9 or 10 thief, backstab my victim in solace sewers, maybe collect a nice set of newbie gear. They would log on their main 25+ mage or cleric try to find me and kill me, and then I would get a tell about "damn, I lost 5 million XP for killing you, what level were you?"
On the surface, there are a couple flaws with taking this system to modern arctic. 1- XP doesn't mean much anymore, the penalty would have to consider ranks or it would be worthless, and given a severe enough level difference you would have to potentially lose rank points to make it hurt. 2- the system didn't account for clans. It was fine and good for keeping 1 vs 1 pvp fair and balanced, but there was nothing to prevent 5 level 20 chars from ganking singular 25+ characters and killing without penalty. To be effective, the penalty system would also have to account for numbers, and penalize pkillers when multiple numbers are used to kill a single player. This might just be too complex to fix in perfect way, but maybe there is some acceptable level where the game would be improved from the status quo.
A few years later, I want to say around 2000, there was the "justice system". I honestly loved this time. A pkiller could run around and gank without any xp loss consequence, but there were flags that tracked the number of kills and in most major towns the guards and guard captain would go agro and start tracking to kill you as soon as you approached if you were flagged as a murderer. I think it was removed due to "abuse", that is someone who was hunted by a clan would go into town and hide near a super-guard mob and let the super-guard kill the geared clanned characters who tried to attack. But that never really seemed like abuse of the system to me, that was it working as intended, it punished the stronger groups who tried to pick on the weaker by giving the weaker players an advantage. Just thinking about it makes me wish it could be brought back to some extent.
Poll
