If it were any threat other than the Borg, that's exactly what he would've done. It's hard to understand just how horrific his ordeal as Locutus was. The Borg broke him. They violated him, enslaved him, made him into a tool for killing thousands of his own people. There's no way he could ever entirely get over such a deep psychological wound.
I would agree with this if not for the episode "I, Borg." Picard had his chance at revenge, at lashing out at the enemy that ravaged him and chose not to. He showed that he was a better man than that. I don't expect him to be a super hero but one of the defining characteristics of Picard is that he never betrays his core principles. The movies pushed that aside, so I suppose the novels are forced to follow suit, but I found it disappointing. I wanted to see him contribute to the solution somehow and instead he actively worked against it. Had anyone listened to him, the Borg would have won. That was my problem. He's not the kind of person to let events swirl around him and he do nothing and he shouldn't be the type of person who would let a race die just because they harmed him. He is better than that. Don't misunderstand, I really liked the books, this was just the sticking point I had with this one.
Well the thing with "I Borg" is that Picard was in charge the whole way, and he basically had the luxury of saying "I'm better than this". And even then, the hope was that Hugh would serve as a virus and spread individuality through the collective. *
In "Destiny" Picard's completely out of control, has been on the ass end of a ass kicking from the Borg repeatedly, and was completely helpless and out of control.
* -- In hindsight, I wonder how much of Picard's "lets pretend to be Locutus" moment was pretend and how much was Locutus slipping back through.