When he's laying down the law to the winter court:
My voice echoed throughout the whole chamber as clearly as if I’d been using a PA system. “All right, you primitive screwheads. Listen up. I’m Harry Dresden. I’m the new Winter Knight. I’m instituting a rule: When you’re within sight of me, mortals are off-limits.” I paused for a moment to let that sink in. Then I continued. “I can’t give you orders. I can’t control what you do in your own domains. I’m not going to be able to change you. I’m not even going to try. But if I see you abusing a mortal, you’ll join Chunky here. Zero warnings. Zero excuses. Subzero tolerance.”
I paused again and then asked, “Any questions?” One of the Sidhe smirked and stepped forward, his leather pants creaking. He opened his mouth, his expression condescending. “Mortal, do you actually think that you can—” “Infriga!” I snarled, unleashing Winter again, and without waiting for the cloud to clear, hurled the second strike, shouting, “Forzare!” This time I aimed much of the force up. Grisly bits of frozen Sidhe noble came pattering and clattering down to the ice of the dance floor.
When I first read this I did a mental double-take. Harry committed murder there. Seriously, he straight up murdered a sapient being for the crime of disagreeing with him, and somehow it's okay because it was a Sidhe, not a human. And nobody calls him out on it. There have been other instances of speciesism in the series, but this takes the cake.
Did he commit legal murder? No. Mab gave approval.
Morally, Harry is in extreme danger, and he knows it. Not long before he did that, he was musing about the danger of power corrupting, one little step at a time. At the time he was thinking about the moral risk of sex with Sarissa, even with consent, under the peculiar circumstances, but it applies more generally. Harry isn't
unaware of the danger.
The problem is that it's also true that Harry probably really
does have to behave that way, and do things like that, to enforce what authority he has in Winter. Not enforcing his authority is suicidal. Literally. He very probably does have to be the Alpha Monster to keep the other monsters at bay. Does that make it OK morally? Not necessarily.
Note that we saw something similar in the short story
Even Hand. What Harry did that Sidhe noble, John Marcone did to a prisoner who started to waste his time with empty bravado. The situation is not
entirely similar, of course. Harry was less in a position of power relative to the others than Marcone was to his prisoners, Marcone had more options available. In each case, though, both men (who are very similar in some ways, psychologically, though they spin in oppositely) issued an order or asked a question, with either a stated or implied threat of death in the even of non-compliance, and then enforced that threat.
By declaring mortal 'off limits' around him, Harry hopes to protect them and himself from traps using mortals, the way Maeve tried to use Sarissa. If the Winter Fae know that the moment they even try something with a mortal to get at Harry, he'll immediately go to DefCon 5 and nuke them on the spot, it provides an incentive not to make that attempt in the first place. That helps avoid things like somefae grabbing Karrin or Butters or Billy and using him/her as a tool in a play against Harry...or so he hopes.
Since the warning has already been
issued, Harry doesn't have to concern himself with things like boundaries or the fae claiming that he's just plucking Karrin's eyes out and it's no concern of Harry's, the warning's already
in place so Harry doesn't need an excuse to act. The fact taht it's a capital offense means that a fae has at least what should be a good reason to think carefully before trying anything 'clever'.
Harry has allowed himself to be put into a position where he may literally have no options other than behaving immorally or dying. It's the latest link in a long chain of bad consequences stemming from a long chain of bad
choices going back to his 16th year, and his ill-advised deal with Lea. It was compounded by later bad choices, especially in
Death Masks. As Uriel keeps trying to pound into him (and is starting to penetrate), bad choices tend to give bad results.
The situation Harry (and Molly) are in now is also glaring proof of the wisdom of Bob's warning to Harry, way way back in Summer Knight, that wise mortal avoid getting mixed up with the Sidhe. At all. For any reason. Note that this is also the traiditional view of the Fae in myth and legend.
Did Harry take a step closer to corruption at the party? Almost certainly. Was it as big a step as it could have been? No, because his options really were limited. But it was a step.