@BingBang:
Big Mom is evil and twisted. She killed Zepo. Luffy is a pirate (normally pirates are evil) and he has not killed anyone.
That we know of. You could easily say that Luffy may have killed dozens between all of the countless Marines he's attacked, guards at Impel Down, etc. Luffy isn't holding back against cannon fodder because he doesn't want to kill them. He's going and attacking like any enemy. He doesn't usually doesn't go overboard, using Gear Fourth on some grunts. But he isn't holding back either.
You could easily say that plenty of these people may have died from their injuries. Look at what happened to Lucci. Yes, he had a very extensive battle with Luffy. But even a tough guy like him was in horrible shape afterword and needed costly medical care to survive. Guys a lot weaker than Lucci have taken similar attacks from Luffy, but have been brushed off to the background.
Here is the thing, though. Oda will never come out and say "Yeah, those guys Luffy attacked got hurt pretty badly, they're crippled for life/dead". And on the flipside he hasn't and likely won't have Luffy ever justify killing or not killing cannon fodder. They aren't important to the story. It's an assumption you can make on whether they die or not, but at the end of the day it's an aspect Oda won't dwell on.
Are we really supposed to believe that every guy Zoro cuts up is fine with some bandages? Or every person that gets crippled by Robin is walking away just fine? Yes or no, it doesn't matter unless it's relevant to the story.
The story right now isn't a "good pirate" versus "bad pirate" story. Luffy is evil to plenty in the One Piece world. Pushing aside people that hate him because of his family, he's a well established criminal who has invaded 3 of the Navy's major establishments, including their HQ. His crew consists of a "Pirate Hunter", a known thief, a girl who allegedly sunk multiple Naval battleships, and soon a former Warlord who betrayed the World Government. On paper, Luffy's a bit of an anarchistic anomaly.
Look at what people said about Roger. They said he had a temper when it came to defending his crew. He wiped out Squard's crew, allegedly. And yet, every instance we've seen of Roger has portrayed him in a manner similar to Luffy.
Is Big Mom's wheel fucked up? Absolutely. It's her weird candy land version of Saw. But, it doesn't cement her in a position where she is absolutely irredeemable. It's not like she's pulling random people off ships and making them spin the wheel. It's used on people in Tottoland, which as we've seen so far, has been used for people invading their territory and someone wanting to break a partnership that resulted in her getting tons of candy for her name protecting an island. It's pretty much only used when someone has directly fucked her over.
Which, while it is psychological torture, a bit more lenient than other Pirates. I mean Pedro was able to come invade the territory a SECOND time after facing punishment. Could you imagine if someone had snuck on the Moby Dick and injured Whitebeard's crew the way the Strawhats have to Big Mom's crew? I don't think Whitebeard would be spinning a wheel for the opportunity to still have some years of your life to life, they'd just be getting a quaking spear in your chest.
And would Whitebeard be an "evil" pirate for that? Nope.
That's what I love about One Piece. It's something that was summed up in the last episode of the One Piece Podcast(which Greg was on). I believe it was Ed who said, "even if they are really bad, in One Piece the villains are still only like 89% evil". It's all about perspective.
I'd actually really like to see some side story from a grunt's perspective of the death and destruction some of the Strawhat's leave in their battles. Something like that would be an interesting thing to see in something like the One Piece Magazines that came out last year.