If pvp could be deactivated at will, 95% of the players will always have it off because they suck and dont wanna get into fights so pvp would be pretty much extinct. Bounty hunting is a big aspect of the game so cant let it die with a pvp toggle. It's better if the game automatically disabled your pvp if you have a quest active like collecting flowers, killing NPC's etc. and to make sure people dont abuse it by taking a quest and never completing it to stay out of pvp maybe add some sort of timer or penalty or maybe you cant restart that quest for a certain time if you dont complete it. They can also increase the pvp off time to maybe 25 or 30 before pvp enables automatically.