No: Harry based his decision on knowing that Lloyd Slate was a monster, and that Mab would also try to monster-ize Harry.
I disagree there, he didn't base his decision on the fact that Slate was a monster. He never said, " gee Lloyd Slate was a monster, I want to be one too.." He did know what Mab would try to do, that's why he planned his suicide before hand.
I'm not saying that Harry has become a monster; but he made that deal in the expectation that he would. He lives now in the hopes that he can resist, but the fear that he won't resist.
That's what he expected, that's why he arranged his death, so that wouldn't happen. Yes, that fear is there for all of us, but just being a wizard with all the power he has, that fear is always present if abused or should be. That is why a certain archangel made sure that he learn some very basic lessons about the soul and free will.
You say that like it's two separate things.
Harry chose to become a monster to save his daughter.
He just chose (what he saw as) the least-monstrous option available.
It is two different things, Harry didn't chose to become a monster, he chose to
take the risk of becoming, based on what Uriel told him as he layed there with his broken back.. If what he does, he does out of love, he will never stray so far from the path that he cannot come back. He arranged for his death, then agreed to become Mab's Knight. The other two options that would give him enough power was taking up a coin and becoming a Denarian.. Yeah, possible he could have rejected it later, but maybe not so easy.. Or becoming a mini-god, with Darkhallow, not that great an option either.. Yes, it was the best of a couple of bad options, otherwise if he did nothing he remained helpless while the Red King sacrificed his daughter, along with him and his grandfather.. Unless you can suggest some better options that Harry didn't explore in Changes that might have been more morally acceptable?