I'm reasonably confident that I've said this already, but just in case, I'll say it again:

There are two arguments against this.

1) Harry blamed himself for Elaine for 10 years, even though that's definitely not his fault, and 10 years is definitely longer than 6 years. So Harry is absolutely capable of thinking something is his fault even thought it really isn't for 6 years.

2) Another reason he didn't realize that Murphy was in the wrong there was because he wasn't thinking about it in those 6 years. Here's an example. There's a math class I'm struggling a bit in, and when I have a test, I end up flunking. Only, plot twist, I actually got the math problems right. What really happened is that the teacher took an irrational dislike to my handwriting and decided to flunk me. When I get the test back, however, I'm uncertain enough of the subject matter that I assume that I genuinely flunked rather than that the teacher gave me the wrong grade. Now, fast forward 6 years, or you know what, fast forward only 1 year. I've been working on my math, and I'm much better now. If I was in that math class now, I would be confident of the material and would realize what the teacher had done. However, if someone said to me, "Hey, you're doing so well now, when just last year you flunked that test," my response would be, "Thanks, I am," rather than, "Well, actually the teacher flunked me for no reason." Unless someone shoved the test under my nose and made me go over all the problems individually, I would never realize that the teacher was the one at fault rather than me. This is because, having no reason to re-evaluate what had happened, I would just go with my initial evaluation. It doesn't mean that the same thing would happen to me now or in the future, and if it did I would realize it, but because I don't really think that much about the past incident, it just never really occurs to me that my original read on the situation could be wrong.

Except even at this stage in the game Harry usually defers to Murphy's judgement...  As to your example of your math test,  I think of the over all consequences of the teacher failing you for penmanship... If the teacher didn't note on the exam as to why you failed, what was the point of failing you for bad penmanship?   If it was just one test in many tests you had taken in the class and your over all grade wasn't in the balance, what you say makes sense.   However say it was the final that the teach failed you on for penmanship... That failure dropped your over all grade considerably, that lower grade messed up your G.P.A. as a result you missed getting a scholarship or getting into the college you desired..  If you knew you had studied, if the teacher gave you no explanation for the failure, I bet you wouldn't be so accepting of the results...  I also think you'd double check the results for any future test you were about to take.. 

Harry didn't blame Murphy,  in his mind I think, because of the resulting slaughter in the police station that she paid a heavy enough price for her mistakes..

Isn't Murphy a Catholic?

She is, and maybe she has a choice before her...  To become a living Valkyrie or a spirit helping helping her father, or beyond to Judgement..  That is if she does die..

I only said anything because you asked. It's like the theme song from friends. "When it hasn't been your day, your week, your month or even your year."

Not my week at all, I had to put one of my dogs down..

No.  It is not a mantle.

Yes and no...  Does the one who holds it gain any physical powers?  No..  It isn't like becoming the Winter Knight or Lady...  However the one who holds it gains great political power, which gives him some power over those who do hold a mantle... One could say, being Blackstaff is a holder of a mantle from what we've seen of it in action...  Holy Knights are kind of mixed, in of themselves they do not have special powers, but the Holy Swords do, which conveys a mantle of power of sorts to the wielder of the Sword.

"Best served cold" is how I've always heard it.

That is what I meant to say.... It's been a difficult last few days and it was early when I wrote it, with only a couple of swallows of coffee...

I still think that they could have found Morgan much sooner if they had wanted to; I can only conclude that they didn't care enough to do so.

But yeah -- WoJ says you're right, Morgan was extra-specially on their ShitList.

Pretty much, but what is the old saying?  "Revenge is a dish best eaten cold.."  Which means essentially waiting for the right moment for maximum effect... So instead of doing it right away, it would wait until in it's sadistic way it would inflict the most pain... 

They just don't care enough.  Humans don't MATTER enough to them; no human does.  Not even one who killed another Naagloshi.

They do when it has a goal, it says outright it will kill every last one of Harry's friends, of those associated with Morgan unless he is turned over to it..  A thing that can focus like that does care, it lives off of fear.. Not caring would make it indifferent.. 

For the same reason she agreed to go vampire hunting a book before this: because she's had it beaten into her by this point that, when it comes to the supernatural, sometimes the right thing to do is to break the law.

Or not so much break the law as some things exist outside of vanilla law, and they have to be dealt with.  That is why the Seven Laws exist, that is why there are Wardens to enforce those laws, harsh penalties for those who break those laws..