Actually, this thread got me thinking about something: Did David ever morph a dolphin?
I think that trapping him as a dolphin might have made him a better person. They use "morph therapy" in 54 to get Jake 'out of his funk." It would still be a risk, but I doubt that he would have gone to the yeerks, because he would have been too happy, especially if they had taken him WAY out to sea first so the morph could have an effect on David's personality.
Tobias said that the hawk instincts affected his personality, made him a stronger person ect.