Plus, he gave Mab a gut check by threatening to imprison her, and she blinked.

Very good point, and his child lived to be 150 I believe when she was murdered, and she had only two kids, one by the mostly sterile White Court.  Or is it they aren't so much sterile as celibate?  Harry is a good example of that, for a healthy man in his prime, how few sexual relationships he has really had.  It has been a topic on the boards for quite some time, people have speculated it was because of shyness, immaturity, a number of things.  But suppose he really is the norm and not the exception among wizards?  Perhaps having all that power and learning how to manipulate it dwindles the sex drive?  Or perhaps there is a real fear that a normal sex life effects the ability to wield their power?   Some do have large families, Luccio and Martha Liberty have stated that, but at least in the case of Luccio, it's other relatives having all the children.  We've no further information on Martha Liberty so we don't know if she ever had kids.

Harry's lack of experience in the bedroom could be due to the fact that for a long time he thought he murdered his first girlfriend, Elaine. It says so in Storm Front.

Harry hurt Uriel by calling him "Uri". The 'el' portion of their names means 'of God'. If verbally omitting 'of God' from his name hurts Uriel, imagine how being deprived of being with God hurts the Denarians. I can't imagine how any of them are still sane after thousands of years without him.

Harry won't kill someone he loves unless the alternative is worse. E.G. Susan.

This is an open window. Eb could have theoretically knocked boots with Leanansidhe, and fathered Margaret. Even though Eb's wife was mortal, nobody has ever said that Margaret was the daughter of Eb's wife.

Margaret may have, on her deathbed, declared for fae and be alive, somewhere in the Never Never.

I don't think it's likely. If Margaret had survived she'd have definitely taken Harry with her, if she were able. But it's a fascinating idea.

Fix is an undeclared changeling and is the Summer Knight. Likewise, Lily was an undeclared changeling and Summer Knight and then Summer Lady.

I'll throw this out there too. Harry owes Mab a favor, plus, he's the Winter Knight, which means he owes all of the Winter Queens unlimited favors, excepting only that he doesn't have to accept any that would hurt the ones he loves.

He also owes Molly a favor from bargaining for the ring in Peace Talks. She warned him to not make an open-ended deal with the fae, but Harry's is remarkably dim in foresight.

Harry owed Lea a debt, and somehow, Mab wound up owning that debt. It's possible she ordered Lea to surrender that debt to her. We don't know what went on behind the scenes. Mab could do the same with Harry's debt to Molly.

Harry's favor to Mab is a conditional, he doesn't have to accept the favor asked. But Molly's debt has no conditions attached to it.

To say nothing of the fact that she could always order Molly to kill Harry. Harry might not have any choice but to kill in self-defense.

My theory is that there's another influence outside the fae courts that stops the fae queens from killing mortals.