In an MMO, Alignment is not really an issue, as opposed to dungeons and dragons where you are restricted to act out your chosen alignment, with penalties if you digress from the boundaries, so it makes it much easier to kill/PK everything in sight. Personally, I like lore and environment (flora and fauna), so I spend the vast majority of my time on plotlines, twists, turns, conspiracies with my character and his interaction with the game world instead of being a murder bot.
Back in the early days of EQ, things were just as likely to kill you as were of them. So initially, fights were as needed and when you were prepared/buffed to do so, for purposes of XP, and if it was green/blue and you had buffs then it died as quickly as possible to get more kills in while buffs were up. And usually, I had already been killed so many times by... let's say "orc centurion" for example, that I had no problem with eliminating every man woman and and child orc in Crushbone... revenge is sweet. Just out and about in the world, though? Idc if it's blue I'm not picking a fight, especially with humanoids that don't KOS me. I'm peaceful until provoked or in an XP area/group.
I tend to kill what I need to, to progress. If I need skins, then I will hunt whatever has them. If I need to find a broach taken by a group of orcs, then I would invis up and check the place out to see if it is in a junk pile in the camp. If not, I would hunt them down until I find the item. Once found, I would leave them to it.
If I have to kill to level and the quests have dried, then I will, but I would rather be adventruing than slaughtering.