See, this is where the definition of "pacifist" is important. Is it "code against killing" or is it "vow of non-violence"? I've always interpreted it as the latter. Fighting just as much as a normal character, but relying on non-lethal damage doesn't make one a pacifist -- unless you consider Spiderman, Batman, and Superman to be pacifists.
Beyond that, anyone who strongly holds values like that does not hang out with folks who regularly violate them. Why is the character a pacifist? It's probably something resembling "because hurting people is wrong". So, why would you spend so much time with folks (other adventurers) that don't share that compunction? Sure, they can use the line "Yeah, but they were all bad people," to justify their actions. If you could do that, you'd be gutting them, too. Instead, the pacifist character should be condemning the other PCs -- or, at least trying to convince them to change their ways.
You can probably excuse a certain amount of "excessive force", but habitual or extreme levels would not be acceptable to any true pacifist.
The other option is that you've taken a religious or philosophic vow to not shed blood. Well, that's pretty much what the 1E cleric class was, mace and all. Clearly, the vow isn't about the morality of beating people up. It's about drawing a line between yourself and others. A legalistic vow like that doesn't really warrant much discussion -- choose a blunt weapon and move on. Morally, were the Knights Templar (don't shed blood) any more pacifists than a random Crusader? Is a spiritual leader (I'm thinking ISIS) who encourages acts of violence without committing them himself any less wicked than those who do his bidding?
Which gets to the deer you used to kill your enemy. If you can compel the deer to act, it's your will that killed the enemy and you bear the weight of that action. Think Jessica Jones, only the deer is Jessica and your "pacifist" is the Purple Man.
And, this is why I say it's difficult to play D&D with a pacifist character, especially if you plan to have much advancement and/or use normal adventures.
A pacifist character might be able to head into a traditional dungeon and sleep everything in sight, take the loot and leave. That covers the bases and aversion to violence doesn't have to map to aversion to theft. Normal XP had, all around, assuming you restrain the slept folks so you don't have to kill them on the way out. Also, don't run out of spells. And... it becomes a lot more difficult to get away with as you go up in level. Plus, there's all that business about the orcs being angry and trying to hunt you down and kill you, anyway.
You can't just tag along with a party that thinks nothing of wanton violence if you have moral qualms with it. So, you're left with adventures that don't involve that.
Which means political or espionage games. I like those, and have used D&D to run them. They just tend to advance very, very slowly. The good news is that those sorts of games scale very well with any level character, so advancement isn't critical -- you can be 5th level with a duchy and it works great.
The bad news is that those sorts of games tend to be very, very sandbox-y, which means it's hard to have set "chapters" for story awards. You're very much at the whim of the GM to notice when a major milestone happens and his judgement about whether it's appropriate to award a whole level at that point. Clever (or lucky) PCs can sometimes bypass a month worth of planning by a GM in a single session. That's not bad, but it does feel very weird to gain two levels in as many sessions. Game systems that use character points of some form tend to smooth out progression much better than D&D for non-combat focused campaigns.
You can do it. It just takes a bit more understanding of the game framework and knowing which knobs to turn.
You could, potentially, get away with it if you played a healer who didn't actually have a moral issue with killing all the orcs, but viewed his pacifism as the price of his healing magic. He's completely forsaken the skills of war to be able to support those who focus on them. Now, you're the Army chaplain who comforts those going to battle in a just war against evil. Depending on your views on moral equivalency, one man's just war is another's terrorist attack or empire-building. You could also play an enchanter, bard, or some such who didn't like getting his hands dirty so never uses actual weapons or direct damage spells.
Maybe the most interesting way of doing a pacifist would be to take advantage of the extremely and explicitly abstract nature of hit points. You'd still have to get party buy-in with the moral issues, but play a monk who tries to avoid conflict but is well trained in self-defense. But... all attacks should be interpreted as non-lethal moves -- throws, pressure points, arm locks, feints, etc. that just wear down your opponent, rather than truly damaging them. Look to things like hap ki do, judo, or even some elements of goju ryu karate. All those forms have some seriously crippling moves, but one-on-one, all have the capability to either wear down your opponent's reserves or put them in a compromising position where you can cause serious pain or dislocate something with a small twitch.
